Pre-Algebra — Numbers & First Variables
The on-ramp: order of operations, signed numbers, fractions/decimals/percents, ratios & proportions, and a first look at variables.
Before algebra, you need to be completely comfortable with numbers — how they combine, the order to combine them in, and the three costumes (fractions, decimals, percents) the same number can wear. This is the on-ramp to the whole Mathematics track. Everything is live — change a number and the results recompute.
- 01 Order of operations (PEMDAS) ELI5: when an expression mixes operations, everyone must agree on the order or we'd get different answers. The rule is PEMDAS: Parentheses, then Exponents,…
- 02 Integers & signed numbers ELI5: integers include the negatives below zero. Two rules trip everyone up: a negative times a negative is positive (−3 × −4 = 12) subtracting a negative adds…
- 03 Fractions, decimals & percents ELI5: these are three costumes for the same number: ½ = 0.5 = 50%. To add fractions, give them a common denominator first; a percent is just "per…
- 04 Ratios & proportions ELI5: a ratio compares two amounts (3 apples to $2). A proportion sets two ratios equal and lets you scale up: if 3 apples cost $2, then 12 apples (4× as many)…
- 05 A first look at variables ELI5: a variable is a letter standing in for an unknown number — the single idea that turns arithmetic into algebra. "Three more than twice a number"…
next course: Algebra 1A — Equations & Lines →