270 core topics
+ 19 prerequisite topics taught
as needed · approximately 92 hours of instruction
including spaced review
An adaptive diagnostic (up to
40 questions) places the student on the course's knowledge
graph - topics already known are credited, and instruction begins exactly
at the learning frontier. Every topic is taught with a worked-example
lesson and auto-graded practice; a topic is mastered at
75%+ and then maintained through spaced reviews on an
expanding schedule. Mixed checks follow every 6 lessons;
each unit ends with a 12-item quiz, and course-wide assessments appear at
25%, 50%, 75%, and 100% mastery. Prerequisite gaps below the course are detected and taught rather
than skipped, so completion certifies the whole tower, not just the top.
| Skip-Counting Puzzles
[H] |
Spot the constant jump and continue the count. |
| Find the Missing Number
[H] |
Work backwards from the total to find the missing part. |
| What Number Am I? (Place Value)
[H] |
Build a number from its hundreds, tens, and ones. |
| Doubling Patterns (Grades 2-4)
[H] |
Each number is twice the one before it. |
| Counting Coins (Grades 2-4)
[H] |
Add up coin values: quarter 25¢, dime 10¢, nickel 5¢, penny 1¢. |
| Making Change (Grades 2-4)
[H] |
Change is what is left after you pay. |
| Fair Sharing with Leftovers
[H] |
Share equally, then count what cannot be split. |
| Elapsed Time (Grades 2-4)
[H] |
Count the minutes from a start time to an end time. |
| Perimeter of a Rectangle (Grades 2-4)
[H] |
Perimeter is the distance all the way around. |
| Counting Odd Numbers (Grades 2-4)
[H] |
An odd number ends in 1, 3, 5, 7, or 9. |
| Adding Consecutive Numbers
[H] |
Add a run of numbers in a row. |
| Working Backwards (Grades 2-4)
[H] |
Undo each step in reverse to find the start. |
| Digit Sums (Grades 2-4)
[H] |
Add up the separate digits of a number. |
| Comparing Numbers
[H] |
Line up place values to see which number is biggest. |
| Repeating Shape Patterns
[H] |
Use the length of the repeat to find any position. |
| Counting Legs (Grades 2-4)
[H] |
Multiply legs per animal, then add the groups. |
| Rows and Columns (Arrays)
[H] |
Equal rows make a multiplication. |
| How Many Can You Buy?
[H] |
Divide your money by the price and ignore the leftover. |
| Age Problems (Grades 2-4)
[H] |
Everyone ages by the same amount each year. |
| Making Equal Groups
[H] |
Divide the total by the group size. |
| Ten and Hundred More
[H] |
Only the tens (or hundreds) digit changes. |
| Rounding to the Nearest Ten
[H] |
Look at the ones digit to decide which way to round. |
| Days and Weeks
[H] |
There are 7 days in each week. |
| Position in a Line (Grades 2-4)
[H] |
Front position and back position add up to one more than the total. |
| Missing Operation
[H] |
Test each operation to see which gives the answer. |
| Halving Numbers
[H] |
Half means splitting into two equal parts. |
| Dozens
[H] |
A dozen means 12. |
| Find the Pattern Rule
[H] |
The rule is the gap between neighbouring terms. |
| Triangular Dot Stacks
[H] |
Stacking rows 1, 2, 3, … makes a triangle of dots. |
| Counting Grid Paths (Grades 2-4)
[H] |
Every shortest path uses the same number of right and down moves. |
| Overlapping Groups (Grades 2-4)
[H] |
Counting both groups counts the overlap twice. |
| Sum-and-Difference Puzzles
[H] |
Guess and check, or split the sum evenly and adjust. |
| Counting Coin Combinations (Grades 2-4)
[H] |
List the possibilities in an orderly way so none are missed. |
| Reversing Digits
[H] |
Swap the tens and ones digits. |
| Biggest Number from Digits
[H] |
Put the biggest digit in the biggest place. |
| Smallest Number from Digits
[H] |
Put the smallest digit in the biggest place. |
| Sum of Odd Numbers (Grades 2-4)
[H] |
Adding the first n odd numbers always makes a perfect square. |
| How Many More? (Grades 2-4)
[H] |
Subtract what you have from what you want. |
| Repeated Halving
[H] |
Each halving divides by 2 again. |
| Logic: Who Is Heaviest?
[H] |
Chain the comparisons together. |
| Counting Squares of All Sizes
[H] |
Do not forget the bigger squares hiding inside. |
| Patterns with Growing Jumps
[H] |
The gap itself gets bigger by a steady amount. |
| Reading a Data Chart
[H] |
Add every category to find the grand total. |
| The Number Just Before
[H] |
Step backwards by the counting amount. |
| Average of Two Numbers
[H] |
The average sits halfway between the two numbers. |
| Digit Riddles
[H] |
Turn the clues into the tens and ones digits. |
| Counting Within a Pattern
[H] |
Count whole blocks first, then the leftover beads. |
| Sharing Money Equally
[H] |
Divide the money by the number of people. |
| Totals from Comparisons
[H] |
Find each amount, then add them. |
| Multiply-then-Add Patterns
[H] |
Apply the same two-step rule to the last term. |
| nth Term of a Sequence
[H] |
Jump straight to any term instead of listing them all. |
| Geometric Sequences (Grades 5-6)
[H] |
Each term multiplies the one before by a fixed factor. |
| When Do Cycles Line Up? (LCM)
[H] |
Events that repeat coincide at their least common multiple. |
| Largest Equal Groups (GCD)
[H] |
The biggest equal split uses the greatest common factor. |
| Counting Handshakes (Grades 5-6)
[H] |
Each pair shakes once - count the pairs. |
| Adding 1 to n Quickly
[H] |
Pair the ends to add a long run instantly. |
| Consecutive Integer Sums
[H] |
The middle number is the average of the run. |
| Find the Missing Value from an Average
[H] |
The total is the average times the count. |
| Percent of a Number (Grades 5-6)
[H] |
Percent means per hundred. |
| Fraction of a Group
[H] |
Split into equal parts, then take the parts you want. |
| Sharing in a Ratio (Grades 5-6)
[H] |
Split the total into equal shares, then group them. |
| Distance = Rate × Time (Grades 5-6)
[H] |
Distance is speed multiplied by time. |
| Elapsed Time Across the Hour (Grades 5-6)
[H] |
Convert both times to minutes, then subtract. |
| Find a Side from the Area
[H] |
Area = length × width, so divide to undo. |
| Counting Rectangles in a Grid (Grades 5-6)
[H] |
A rectangle is fixed by choosing two vertical and two horizontal lines. |
| Diagonals of a Polygon (Grades 5-6)
[H] |
Each vertex connects to all but itself and its two neighbours. |
| Reversed-Digit Differences
[H] |
The difference is always a multiple of 9. |
| Counting Multiples (Grades 5-6)
[H] |
Divide and drop the remainder. |
| Units Digit of a Power (Grades 5-6)
[H] |
Last digits repeat in a short cycle. |
| Spotting Multiples of 3
[H] |
A number is a multiple of 3 when its digit sum is. |
| Multi-Step Working Backwards
[H] |
Reverse the steps in the opposite order. |
| Chickens and Rabbits
[H] |
If all were chickens, every extra pair of legs is a rabbit. |
| How Many in Neither Group?
[H] |
Subtract the union from the total. |
| At Least One (Inclusion-Exclusion)
[H] |
Add the groups but subtract the overlap once. |
| Systematic Counting of Numbers
[H] |
Count choices for each place and multiply. |
| Choosing a Team (Combinations)
[H] |
Order does not matter when you choose a group. |
| Ordered Arrangements (Permutations)
[H] |
When order matters, multiply the shrinking choices. |
| Perfect Squares in a Range
[H] |
Perfect squares are 1, 4, 9, 16, 25, … |
| Counting Factors (Grades 5-6)
[H] |
Factors come in pairs that multiply to the number. |
| Adding Unlike Fractions (Grades 5-6)
[H] |
Rewrite over a common denominator first. |
| Leftovers When Sharing
[H] |
The leftover is the remainder of the division. |
| Angle Between Clock Hands
[H] |
The minute hand moves 6° per minute; the hour hand 0.5°. |
| Sum of an Arithmetic Series
[H] |
Average the first and last term, then multiply by how many. |
| Insert the Operation
[H] |
Test each operation until one hits the target. |
| The Value of a Digit
[H] |
A digit's worth depends on its place. |
| Rounding to the Nearest Hundred
[H] |
Look at the tens digit to decide the direction. |
| Scaling a Recipe (Grades 5-6)
[H] |
Find the per-person amount, then multiply. |
| Best Buy (Unit Price)
[H] |
Compare price per single item. |
| Arranging Letters with a Repeat
[H] |
A repeated letter halves the count of arrangements. |
| Reversed-Digit Sums
[H] |
A number plus its reverse is 11 times the digit sum. |
| The Next Perfect Square
[H] |
Find the square root, round up, and square again. |
| Finding the Median (Grades 5-6)
[H] |
The median is the middle value once sorted. |
| Finding the Mode (Grades 5-6)
[H] |
The mode is the value that appears most often. |
| Finding the Range (Grades 5-6)
[H] |
The range is the gap from smallest to largest. |
| Percent Increase (Grades 5-6)
[H] |
Add the extra percent onto the original. |
| Least Common Multiple (Grades 5-6)
[H] |
The smallest number both divide into. |
| Greatest Common Factor (Grades 5-6)
[H] |
The largest number that divides both. |
| Simple Probability (Grades 5-6)
[H] |
Probability is favourable outcomes over total outcomes. |
| Counting Divisible Numbers
[H] |
Check each number for an even split. |
| Average Speed (Grades 5-6)
[H] |
Average speed is total distance over total time. |
| Summing an Arithmetic Series
[H] |
Number of terms times the average of the ends. |
| Summing a Geometric Series
[H] |
Use the closed form a(rⁿ − 1)/(r − 1). |
| Square-Number Patterns
[H] |
When first differences grow steadily, the rule is quadratic. |
| Sum of the First n Squares
[H] |
There is a formula: n(n + 1)(2n + 1) ÷ 6. |
| Choosing Three (Combinations)
[H] |
Divide the ordered count by the arrangements of the chosen items. |
| Ordered Selections
[H] |
Multiply the shrinking list of choices, one per position. |
| Sum of Even Numbers (Grades 7-8)
[H] |
Factor out the 2 and use the triangle formula. |
| Polygon Diagonals (Grades 7-8)
[H] |
Each vertex joins all but itself and its two neighbours. |
| Interior Angle Sum
[H] |
Split the polygon into triangles from one vertex. |
| Interior Angle of a Regular Polygon (Grades 7-8)
[H] |
Share the angle sum equally among the vertices. |
| Pythagorean Triples
[H] |
In a right triangle, leg² + leg² = hypotenuse². |
| Working Together (Grades 7-8)
[H] |
Add the rates, not the times. |
| Mixture Percentages
[H] |
Percent juice is juice ÷ total, times 100. |
| Percent of a Percent
[H] |
Apply the two percents one after another. |
| Three-Part Ratios (Grades 7-8)
[H] |
Total parts set the size of one share. |
| Age Puzzles with Algebra
[H] |
Set up an equation for the future ages. |
| Coin Value Puzzles
[H] |
Assume all one coin, then account for the extra value. |
| Remainders of Powers (Grades 7-8)
[H] |
Remainders of powers fall into a repeating cycle. |
| Sum of Divisors (Grades 7-8)
[H] |
Add every factor, pairing them for speed. |
| GCF × LCM = Product
[H] |
The product of two numbers equals GCF times LCM. |
| Sums of Consecutive Integers (Grades 7-8)
[H] |
Subtract the fixed 'staircase' extra, then divide. |
| Guaranteeing a Match (Pigeonhole)
[H] |
One more than the number of colors forces a repeat. |
| Distributing Identical Items
[H] |
Place dividers in the gaps between items. |
| Binomial Coefficients (Grades 7-8)
[H] |
C(n, k) counts unordered selections of k from n. |
| Shortest Lattice Paths
[H] |
Every path is an arrangement of right and up moves. |
| Counting Ways to Make Change
[H] |
Build up the count coin type by coin type. |
| Weighted Averages (Grades 7-8)
[H] |
Weight each average by its group size. |
| Average After Adding a Value
[H] |
Rebuild the total, then divide by the new count. |
| Fibonacci-Style Sequences (Grades 7-8)
[H] |
Each term is the sum of the previous two. |
| Constant Second Differences
[H] |
Extend the differences to extend the sequence. |
| Fraction-of-Remainder Problems
[H] |
Each fraction acts on what is left, not the original. |
| Meeting-in-the-Middle
[H] |
They close the gap at the sum of the speeds. |
| Up Then Down by the Same Percent
[H] |
The result is below the start - the percents apply to different bases. |
| Area of an L-Shape
[H] |
Subtract the missing rectangle from the whole. |
| Perimeter with Algebra
[H] |
Turn the perimeter into an equation for the width. |
| Similar Figures
[H] |
Corresponding sides share one scale factor. |
| Multiplying Powers (Grades 7-8)
[H] |
Same base: add the exponents. |
| Powers of Ten
[H] |
Multiplying powers of ten adds the exponents (and the zeros). |
| Checkerboard Coloring
[H] |
On an odd board the corner color has one extra square. |
| Triangulating from a Vertex
[H] |
Diagonals from one vertex cut an n-gon into n − 2 triangles. |
| The Next Multiple
[H] |
Divide, drop the remainder, then step up one. |
| Complement Probability
[H] |
The chance of 'not' is one minus the chance of 'yes'. |
| Average of 1 to n
[H] |
For an evenly spaced list, the mean is the middle value. |
| Counting Coprime Numbers
[H] |
Count values sharing only the factor 1 with n. |
| Remainder of a Triangular Sum
[H] |
Add with the formula, then take the remainder. |
| Distance Between Points (Grades 7-8)
[H] |
The distance is the hypotenuse of a right triangle. |
| How Many Terms?
[H] |
Count the steps, then add one for the start. |
| Ordered Pairs with a Fixed Sum
[H] |
The first number can be anything from 1 up to N − 1. |
| Median of an Even List
[H] |
With no single middle, average the two central values. |
| Trailing Zeros of a Factorial (Grades 7-8)
[H] |
Count the factors of 5 in the product. |
| The Row That Is Not Shown
[H] |
Subtract the rows you can see from the grand total to find the row that is missing. |
| Boxes of Ten and Loose Ones
[H] |
Ten loose ones trade for one box of ten, so a count can be repacked either way. |
| A Number from Digit Clues
[H] |
Test the clues one at a time against each candidate until only one number survives. |
| How Many Numbers in Between?
[H] |
The whole numbers strictly between two numbers are counted without either end. |
| The Missing Part of a Total
[H] |
Add every part you can see and take that away from the total to find the part left out. |
| Balancing Two Sides
[H] |
Total the side you can work out, then find what the other side needs to match it. |
| A Two-Step Number Machine
[H] |
Run the steps forwards when the start is known and undo them in reverse when it is not. |
| Equal Jumps on a Number Line
[H] |
Equal jumps multiply, so the distance traveled is the jump size times the number of jumps. |
| The Missing Digit in a Sum
[H] |
Work out the whole two-digit number first, then read off the digit that the box hides. |
| Gaps in a Skip Count
[H] |
Find the constant jump from any two neighbouring terms, then fill the gap or extend the count. |
| Numbers Two Counts Share
[H] |
A number said by both counts must fit both jumps, so step along one count and test it against the other. |
| Growing a Dot Array
[H] |
Equal rows multiply, so adding or completing rows changes only the number of rows. |
| Matching a Sentence to a Picture
[H] |
A dot array can be written as a product or as a repeated addition of the row size. |
| Which Pile Is Biggest?
[H] |
Turn every description into a single number first, then compare the numbers. |
| How Many More for an Equal Share
[H] |
Count up from the total to the next multiple of the group size to see how many more are needed. |
| Cartons Needed and the Last Carton
[H] |
A part-filled carton still counts as a carton, so any leftover forces one extra box. |
| Counting Round a Circle
[H] |
Handing things round a circle repeats with the number of seats, so a remainder names the seat. |
| Moving on a Number Chart
[H] |
One step down a number chart adds a whole row and one step right adds one. |
| Reading a Dot on a Number Line
[H] |
Find the size of one space first, then count spaces from a label you can read. |
| Odd or Even Without Adding
[H] |
Parity follows a rule of its own, so a sum can be judged odd or even before it is worked out. |
| Which One Needs Regrouping?
[H] |
Only the ones digits decide whether a two-digit sum or difference has to regroup. |
| Two Cards from a Row of Five
[H] |
Search a small set in order so every pair is tested once and none is tested twice. |
| A Missing Cell in a Times Table
[H] |
Each cell of a times table is its row label multiplied by its column label. |
| Same Total, Different Rows
[H] |
Doubling the number of rows and halving the row size leaves the total untouched. |
| A Fraction of a Group
[H] |
A unit fraction of a set is one of the equal parts the set is split into. |
| Filling and Doubling a Ten Frame
[H] |
A ten frame shows at a glance how far a count is from ten and from a teen number. |
| Counting Colors in a Repeating Strip
[H] |
A repeating strip is fixed by its unit, so any place is found from the remainder after dividing by the unit length. |
| A Pattern with Two Different Jumps
[H] |
When a pattern alternates two jumps the rule only repeats every second step. |
| Swapping One Thing for Another
[H] |
A balance gives an exchange rate, and every further swap multiplies or divides by that rate. |
| Who Owns Which Thing
[H] |
With one thing each, naming another child's thing removes it from everybody else. |
| Placing Four Children in a Line
[H] |
Fix the places a clue names outright, then fit the joined pairs into the gaps that are left. |
| Numbers Made from Digit Cards
[H] |
Count the choices place by place, remembering that a used card is gone and that a leading zero is not allowed. |
| Counting Outfits
[H] |
Each choice in one list can meet every choice in the other, so the counts multiply. |
| Handshakes Around a Table
[H] |
Every pair meets once, so count the pairs and halve only when the two directions are the same event. |
| The Fewest Coins
[H] |
Take as many of the largest coin as fit, then move down the list, and the count cannot be beaten. |
| Paying from a Price List
[H] |
Total the purchase first and subtract once, rather than making change item by item. |
| Later and Earlier on a Clock Face
[H] |
Move the minute hand in whole quarters and carry an hour whenever it passes the twelve. |
| Reading a Timetable
[H] |
A row gives a length by subtraction and two rows give a gap the same way. |
| A Picture Graph with a Key
[H] |
When one picture stands for several things, every row must be multiplied by the key before it means anything. |
| Comparing Rows of a Tally Chart
[H] |
Count each gate of five as five, write the four totals down, and only then compare them. |
| Mixed Numbers That Regroup
[H] |
Add and subtract mixed numbers by rewriting one whole as a fraction whenever the fraction parts will not fit. |
| Comparing Fractions Against a Benchmark
[H] |
Rewrite every fraction with one common denominator, or measure each against a benchmark, before deciding which is bigger. |
| Multiplying and Dividing Decimals by Powers of Ten
[H] |
Multiplying by ten moves every digit one place to the left, and dividing moves it one place to the right. |
| A Fraction of a Measurement
[H] |
Convert the measurement into the unit the answer wants, then take the fraction of it - and take the second fraction of what is left, not of the original. |
| Money in Several Steps
[H] |
Work in cents so nothing rounds, find every subtotal before the total, and reverse the same chain when a single price is the unknown. |
| Sharing Into Fractional Servings
[H] |
Dividing by a fraction asks how many of those pieces fit, so the count is larger than the amount you started with. |
| Ratios Before and After a Change
[H] |
Write each quantity as so many equal parts, then let the one extra fact pin down the size of a part. |
| Reading a Map Scale
[H] |
A scale is a rate: multiply to go from the drawing to the real world and divide to come back. |
| Rates With a Unit to Convert
[H] |
Put both quantities into the same unit of time before you multiply, and never add two rates that are measured per different unit. |
| From a Ratio to a Fraction or a Percent
[H] |
A ratio compares part with part, so the denominator of the matching fraction is the SUM of the parts. |
| Discount, Then Tax
[H] |
Each percent change acts on the price in front of it, so the changes are applied one after another and never simply added. |
| Finding the Whole From a Percent
[H] |
When the part is known and the whole is wanted, divide by the percent instead of multiplying by it. |
| Percents Across Two Groups
[H] |
A percent is always a percent OF something, so two groups of different sizes cannot have their percents averaged. |
| Percents From a Data Table
[H] |
Read the count from the table, divide by the total that belongs with it, and rebuild the total whenever the data changes. |
| The Area of a Border
[H] |
A border is the difference of two rectangles, and its width is added twice to each dimension - once at each end. |
| Area and Perimeter of an L-Shape
[H] |
Cutting a corner out of a rectangle takes area away but leaves the perimeter unchanged. |
| Tiling a Floor and Paying For It
[H] |
Match the units before counting tiles, then round the number of BOXES upward because part of a box cannot be bought. |
| Same Perimeter, Different Areas
[H] |
List every whole-number rectangle that fits the condition and compare, because the extreme is always at the most square shape. |
| Volume of a Box, Forwards and Backwards
[H] |
Volume is the area of the base times the height, so a missing dimension is found by dividing the volume by the other two. |
| Water Levels and Displacement
[H] |
The volume of water is base area times depth, so pouring or sinking something changes the depth by that volume divided by the base area. |
| Painted Cubes
[H] |
Sort the small cubes by where they sit: corners have three painted faces, edges two, face centers one, and the inside none. |
| Working Out a Timetable
[H] |
Add the hours and the minutes separately, then trade sixty minutes for an hour, and count the gaps rather than the events. |
| Buses, Waits and Deadlines
[H] |
Departures every k minutes are a list of multiples, so a wait is what is left over and a count of departures is one more than the number of gaps. |
| The Score You Still Need
[H] |
Turn the target average into a required TOTAL, then subtract the total already scored. |
| Putting Two Averages Together
[H] |
Rebuild each group's total before combining, because a bigger group pulls the joint average towards its own. |
| When One Value Changes
[H] |
Work with the total: swapping a value changes the total by the difference, and removing values changes the count as well. |
| The Digit That Makes It Divide
[H] |
Use the digit tests: threes and nines look at the digit sum, fours look at the last two digits, and two tests together must both pass. |
| Rectangles With a Given Area
[H] |
Each rectangle with whole-number sides is one factor PAIR of the area, so counting rectangles means pairing the factors up. |
| Numbers With a Given Remainder
[H] |
Numbers leaving a fixed remainder form their own ladder: start at the remainder and step up by the divisor. |
| Hunting for Primes
[H] |
Test a candidate by dividing only by primes up to its square root, and remember the composites that look prime. |
| Growing Matchstick Patterns
[H] |
A pattern that grows by the same amount each time is the first figure plus that amount one time fewer than the figure number. |
| Position in a Repeating Pattern
[H] |
Divide by the length of the cycle: the remainder names the position inside the block and the quotient counts the whole blocks. |
| Sequences With Two Rules Taking Turns
[H] |
Find the two rules by looking at the gaps in turn, then continue the pattern by alternating them strictly. |
| Counting Numbers With a Digit Rule
[H] |
Count place by place: decide how many digits may sit in each position, then multiply, and treat a leading zero as forbidden. |
| Counting Choices With a Restriction
[H] |
Multiply the number of choices at each stage, then subtract exactly the combinations that the restriction forbids. |
| Counting the Games in a Tournament
[H] |
A knockout needs one match per team eliminated, while a round robin needs one game per PAIR of teams. |
| Routes Across a Street Grid
[H] |
Write on each crossing the number of ways to reach it, adding the crossing above and the crossing to the left. |
| Who Owns Which Pet
[H] |
Cross off every pairing a clue forbids and the survivors fall into place one at a time. |
| Putting a Race in Order
[H] |
Build the finishing order from the strongest clue outwards, and use the clues that rule a position out to close the gaps. |
| Balancing Scales by Swapping
[H] |
A balance says two collections weigh the same, so either side may be swapped for the other wherever it appears. |
| Direct and Inverse Variation
[H] |
Decide whether the product or the quotient of the two quantities is the constant, then rebuild the missing value. |
| Scale Factors for Area and Volume
[H] |
A length ratio of k makes areas grow by k squared and volumes by k cubed, and every one of those steps is reversible. |
| Rates Whose Units Must Be Reconciled
[H] |
Put every rate in the same unit of time before it is scaled, reversed, or added to another rate. |
| Ratios That Shift
[H] |
Name the size of one ratio part, then write the change as an equation in that one unknown. |
| Two Percent Changes in a Row
[H] |
Multiply the change factors instead of adding the percents, and reverse the same product to recover a hidden change. |
| Working Back to the Original Price
[H] |
Divide by the change factor to undo a percent change, and strip away any flat amount before you divide. |
| Percent More and Percent Less
[H] |
The two directions of a comparison measure against different bases, so they never give the same percent. |
| Percent Change in Area
[H] |
Area is a product, so each dimension contributes its own factor and the factors multiply. |
| Variables on Both Sides
[H] |
Clear the brackets or the denominators first, then gather the variable on one side and the constants on the other. |
| Counting the Integer Solutions
[H] |
Solve for x first, then count the integers inside the interval by subtracting the endpoints and adding one. |
| The Sign Flip in an Inequality
[H] |
Dividing or multiplying an inequality by a negative number reverses the direction of the sign. |
| Turning a Sentence into an Equation
[H] |
Name the unknown, write each phrase as it is spoken, and only then solve. |
| Adding and Subtracting Two Equations
[H] |
Combine the two equations so that one variable disappears, and stop as soon as the quantity asked for appears. |
| Two Purchases, Two Unknown Prices
[H] |
Two shopping baskets are two equations, and the difference or the sum of the baskets is often the fastest route. |
| Power and Quotient Laws for Exponents
[H] |
Rewrite every term over one common base, then add exponents for a product and subtract them for a quotient. |
| Zero and Negative Exponents
[H] |
A negative exponent is a reciprocal, not a negative number, and anything to the zero power is one. |
| Simplifying a Square Root
[H] |
Pull the largest perfect square out of the radicand, and only add radicals that already share the same radicand. |
| Arithmetic in Scientific Notation
[H] |
Handle the number parts and the powers of ten separately, then renormalize so the leading number sits between 1 and 10. |
| The Pythagorean Theorem in Context
[H] |
Name the hypotenuse first, because the theorem treats it completely differently from the two legs. |
| The Diagonal of a Box
[H] |
Apply the theorem twice: once across the base, once up to the far corner. |
| Area and Perimeter of a Right Triangle
[H] |
The two legs are the base and the height, so the area needs the legs while the perimeter needs the hypotenuse as well. |
| Measuring by Shadows
[H] |
Objects and their shadows at the same moment form similar right triangles, so height over shadow is a constant. |
| A Line Drawn Parallel to a Side
[H] |
A line parallel to one side cuts off a triangle similar to the whole one, so every length is in the same ratio and every area in its square. |
| Parallel Lines with Algebra
[H] |
Decide whether the two marked angles are equal or supplementary, then write that as an equation. |
| Exterior Angles of a Triangle
[H] |
An exterior angle equals the sum of the two interior angles it is not next to, which turns three-angle problems into two-angle ones. |
| Chasing Angles Through Isosceles Triangles
[H] |
Equal sides force equal base angles, and each new triangle in the figure gets its own angle sum of 180. |
| Surface Area of a Prism
[H] |
Add the areas of the faces the solid actually shows, and remember that gluing two solids hides two faces. |
| Volume of a Cylinder
[H] |
The volume of a cylinder is the area of the circular base times the height, so the radius counts twice and the height once. |
| Volume of a Composite Solid
[H] |
Break the solid into boxes, and treat poured or displaced water as a volume that keeps its size while its shape changes. |
| Two Draws Without Replacement
[H] |
The second draw happens in a smaller bag, so both the favourable count and the total count drop by one. |
| Independent Events in Stages
[H] |
Independent stages multiply, an OR needs the overlap subtracted once, and at least one is easiest through its complement. |
| Totals on Two Dice
[H] |
Count ORDERED pairs of faces, because the two dice are distinguishable even when they look alike. |
| Counting Numbers with a Restriction
[H] |
Fill the most restricted position first, then count the choices left for the others. |
| Arrangements With Two Items Tied or Split
[H] |
Glue two items into one block to force them together, and subtract that count from the total to force them apart. |
| Committees With a Condition
[H] |
A committee is an unordered choice, and at least one is counted as everything minus none. |
| Sequences Built by a Repeated Rule
[H] |
Apply the rule one step at a time going forwards, and undo it in the opposite order going backwards. |
| Which Term Is It?
[H] |
Invert the rule for the nth term: subtract the start, divide by the step, and add one back on. |
| Numbers With Given Remainders
[H] |
A remainder condition repeats every modulus, so two conditions repeat together every lcm of the two moduli. |
| Units Digits of Powers
[H] |
Units digits of powers repeat in a short cycle, so the exponent only matters through its remainder. |
| GCF and LCM from Prime Factors
[H] |
Compare the two numbers prime by prime: the gcf takes the smaller exponent and the lcm takes the larger. |