Basic Math
From place value to percentages and geometry, drawn out so a fraction is a pizza being cut and a percent is 100 shaded squares.
16 units · 111 topics · 555 questions
What each digit in a big number is actually worth, and how to compare, order, round, and estimate with confidence.
What Place Value Really Means · Reading and Writing Big Numbers · Comparing Multi-Digit Numbers · Ordering Numbers from Least to Greatest · +2 more
Joining and taking away made visual — how carrying and borrowing move actual ones, tens, and hundreds around.
What Addition and Subtraction Really Mean · Regrouping: Bundling Ten Ones into a Ten · Adding Multi-Digit Numbers with Regrouping · Subtracting Across Zeros · +1 more
Multiplication as equal groups and as a rectangle's area, from times tables to multi-digit products.
What Multiplication Really Means · Arrays and the Area Model · Times Tables as Patterns · The Distributive Property of Multiplication · +3 more
Division as real sharing, worked all the way through long division, with remainders that finally make sense.
What Division Really Means · Division as the Opposite of Multiplication · Long Division Step by Step · Dividing a Multi-Digit Number by a One-Digit Number · +2 more
The building blocks of whole numbers: factors, multiples, primes, and the two tools — GCF and LCM — built from them.
What a Factor Is · What a Multiple Is · Prime and Composite Numbers · Finding Primes with the Sieve of Eratosthenes · +2 more
What a fraction actually is, seen as pieces being cut, compared, simplified, and rewritten as mixed numbers.
What a Fraction Actually Is · Fractions on a Number Line · Equivalent Fractions: the Same Amount, Cut Differently · Simplifying Fractions to Lowest Terms · +4 more
Why fractions need a common denominator before they can be added or subtracted, worked out piece by piece.
Adding Fractions with the Same Denominator · Adding Fractions with Different Denominators · Subtracting Fractions with Different Denominators · Adding and Subtracting Mixed Numbers · +1 more
Multiplying fractions as shrinking, and dividing by a fraction as counting how many pieces fit inside.
Multiplying a Fraction by a Whole Number · What It Means to Multiply Two Fractions · Multiplying Mixed Numbers · What It Means to Divide by a Fraction · +2 more
Decimals as another way to write a fraction, compared, rounded, and pushed through all four operations.
What a Decimal Actually Is · Decimal Place Value · Comparing and Ordering Decimals · Rounding Decimals · +4 more
A percent as literally out of 100, turned into discounts, tips, and how much something grew or shrank.
What a Percent Actually Means · Converting Between Percents, Decimals, and Fractions · Finding a Percent of a Number · Finding What Percent One Number Is of Another · +3 more
Comparing two amounts the same way every time — ratios, unit rates, comparison shopping, and scaling recipes and maps.
What a Ratio Actually Compares · Equivalent Ratios · Unit Rates · Comparison Shopping with Unit Rates · +2 more
Negative numbers as a walk along a number line, and the grid where two number lines cross to locate any point.
What a Negative Number Actually Means · Comparing and Ordering Negative Numbers · Adding and Subtracting on a Number Line · Subtracting a Negative Number · +3 more
Why the same expression needs one agreed-upon order, or two people get two different right-looking answers.
Why Order of Operations Rules Even Exist · Parentheses First · Multiplication and Division Before Addition and Subtraction · Working Through Multi-Step Expressions
Angles, shapes, perimeter, area, and volume, built up piece by piece until a circle unrolls into a triangle.
Points, Lines, Rays, and Angles · Measuring Angles with a Protractor · Types of Angles · Classifying Triangles · +15 more
Converting between units, tracking elapsed time, and handling money down to the last coin of change.
Converting Between Units of Length · Converting Between Units of Weight and Capacity · Elapsed Time · Making Change and Adding Money Amounts · +1 more
Turning a pile of numbers into a bar graph, a line graph, or a single number that sums it all up.
Reading and Making Bar Graphs · Reading Line Graphs · Pictographs · Line Plots · +2 more