The short version Multiplication is a fast way to add equal groups. 4 × 3 means four groups of three, which is 3 + 3 + 3 + 3 = 12. The numbers you multiply are called factors. The answer is the product. Order doesn’t change the answer: 4 × 3 and 3 × 4…
The short version The median is the middle value of a set of numbers once you put them in order from smallest to largest. Odd count: the median is the single number in the middle. Even count: add the two middle numbers and divide by 2. Sorting first is not optional. Most wrong answers come…
The short version The six types of graphs kids meet in school are bar graphs, line graphs, pictographs, circle graphs, histograms and scatter plots. Pick by the question you’re answering. Comparing separate groups is a bar graph. Tracking change over time is a line graph. Showing parts of one whole is a circle graph. Bar…
The short version Going from a bigger unit to a smaller one, multiply. Going from a smaller unit to a bigger one, divide. That one rule covers nearly every conversion your kid will see. Customary units (inches, pounds, gallons) use numbers you have to memorize. Metric units (meters, grams, liters) all step by 10, so…
The short version The surface area of a rectangular prism is 2(lw + lh + wh), where l is length, w is width and h is height. It works because the box has three pairs of matching faces. Find the area of one face from each pair, add the three, then double it. The answer…
The short version Calculus is the math of change. It answers two questions: how fast is something changing right now, and how much has piled up over time. The first question is a derivative. The second is an integral. Those two ideas are the whole subject. Most students meet calculus in 11th or 12th grade,…
The short version Euler’s number, written e, is about 2.71828. It never ends and never repeats, the same way pi doesn’t. It came out of a question about compound interest: what happens to your money if the bank adds interest every second instead of once a year? e is the base of natural logarithms, so…
The short version Subtraction is taking one number away from another. The answer is called the difference. It has three jobs in school math: take away, compare two amounts, and find a missing part. Subtraction undoes addition. If 7 + 5 = 12, then 12 – 5 = 7 and 12 – 7 = 5….
The short version To convert fractions to decimals, divide the top number by the bottom number. 3 ÷ 8 = 0.375, so 3/8 = 0.375. Faster option: if the bottom scales up to 10, 100 or 1,000, scale the top by the same amount and read the decimal straight off. 7/20 becomes 35/100, which is…
The short version There are four types of fractions based on the numbers themselves: proper, improper, mixed and unit. There are three more that describe how two fractions relate: like, unlike and equivalent. Proper means the top is smaller than the bottom, so the value is under 1. Improper means the top is equal to…