- 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±
Signed numbers: the sign rule in 5 lines
Same sign = positive, different signs = negative. One rule for multiplication and division.
- Middle school⚡Mental math√
Simplify √a to b√c: pull out the largest perfect square
√72 = √(36 × 2) = 6√2. Find the largest perfect square dividing a and pull it out.
- Middle school⚡Mental math🔬
Scientific notation: a × 10^n with 1 ≤ |a| < 10
A number between 1 and 10, times a power of 10. Handle huge and tiny numbers with ease.
- Middle school⚡Mental math²
Powers: product, quotient, power of a power
aⁿ × aᵐ = aⁿ⁺ᵐ. aⁿ / aᵐ = aⁿ⁻ᵐ. (aⁿ)ᵐ = aⁿˣᵐ. The 3 rules that simplify everything.
- 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 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💯
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 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➗
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.
- Middle school⚡Mental math↔️
Decimal to fraction and back: the quick swap
0.75 = 3/4. 1/8 = 0.125. Two reflexes to switch forms in 3 seconds.