- Middle school⚡Mental math🎯
Squaring a number ending in 5, without a calculator
Multiply the left part by itself + 1, stick 25 at the end. Done.
- Middle school⚡Mental math%
Percent ↔ decimal: shift the decimal point 2 places
20% = 0.20. 3.5% = 0.035. The 2-second rule that unlocks everything else (proportionality, discounts, tax).
- Middle school⚡Mental math🎩
Multiply two numbers near 100 in 5 seconds
96 × 97 = ? Two differences, one multiplication, one concatenation. The mental magician's trick.
- Middle school⚡Mental math✋
Multiply by 5: halve it, then multiply by 10
Multiplying by 5 is a classic trap: go through the half, then add a zero. Twice as fast.
- Middle school⚡Mental math💯
Multiply by 25: divide by 4, add two zeros
An ultra-efficient variant of the ×5 trick. Works for ×50, ×250 and ×2500 too.
- Middle school⚡Mental math⚡
Multiply any 2-digit number by 11 in 3 seconds
A classic but mind-blowing trick: add the two digits, slide them in the middle, done.
- Middle school⚡Mental math➗
Divide by 5: double it, then divide by 10
The reverse of the ×5 trick: double the number and drop a zero (or shift the decimal). Instant.
