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🔢 Numbers
Numbers are where math begins: place value, fractions, primes… Master these and algebra and geometry get much easier.
- 01🔢Place ValueThe same digit is worth ten times more every step it moves left.
- 02🍕FractionsHalf a pizza, a quarter of a cake — fractions are the numbers you get by cutting things into equal parts.
- 03🔍Prime NumbersNumbers divisible only by 1 and themselves — the atoms every other whole number is built from.
- 04➕AdditionCombine two groups into one — the friendliest operation, happy to be done in any order.
- 05➖SubtractionTake some away, or measure the gap — subtraction plays addition backwards, so check it by adding back.
- 06✖️MultiplicationThe same number added many times? Multiplication writes it in one line — and opens the door to the distributive law.
- 07➗DivisionShare fairly or pack in groups — division unpacks multiplication, one digit at a time.
- 08🔟DecimalsA price of 3.5, a height of 1.62 — the decimal point extends the place-value story to the right.
- 09💯PercentagesHow many out of one hundred — a common denominator of 100 makes everything easy to compare.
- 10🤔EstimationSay a rough number first, compute exactly second — estimation is a pocket-sized checker and a wallet guard.
- 11🌡️Positive & Negative NumbersThree below zero, two floors down, five in debt — numbers less than zero record the opposite direction.
- 12🧱Factors & MultiplesWho divides 12 exactly, and what does 12 divide? — the brick-building manual for whole numbers.
- 13🎯RoundingA population of 13.953 million becomes "about 14 million" — rounding keeps the digits that matter.
- 14🥤Ratios & Proportion3 scoops of concentrate to 2 of water, 20 candies split 3:2 — a ratio is a fixed recipe for comparing.
- 15🔬Scientific NotationLight covers 300,000,000 meters per second — when numbers outgrow the page, scientists write them like this.
- 16◼️Squares & CubesA side-5 square takes 25 tiles, a side-5 cube holds 125 — multiplying a number by itself has a shape.
- 17🍰Fraction ArithmeticAdd and subtract after matching denominators, multiply straight across, divide by flipping — each fraction operation has its own rule.
- 18📈Percentage ChangeIs a rise from 50 to 75 a 25% or a 50% increase? Change is always measured against the original number.
- 19🪜Order of OperationsThe same expression gives 20 computed left to right and 14 by the rules — brackets first, then powers, then multiply and divide, add and subtract last.
- 20♻️Fractions ↔ Decimals ↔ PercentsThree outfits for one number — divide, shift the point, simplify, and switch any time.
- 21🌱Square RootsSquaring asks "what do you get", the square root asks it backwards — plus a squeeze trick for estimating.
- 22🔌Binary NumbersComputers know only 0 and 1, yet they compute everything — the secret is a number system with just two digits.
- 23🗿Roman NumeralsSeven letters that carried three thousand years — how to read and write Roman numerals, and why they finally lost to place value.
- 24🍱Mixed Numbers & Improper FractionsOne number, two costumes — mixed numbers read nicely, improper fractions calculate nicely, and switching between them takes only a step or two.
- 25🧮Decimal ArithmeticLine up the point to add and subtract, count decimal places to multiply, shift the point to divide — three habits cover everything.
- 26🚪Odd and Even NumbersSpot odd or even from the last digit alone — plus how oddness behaves under adding, subtracting and multiplying.