Trick #1: Multiply Any Two-Digit Number by 11 in Seconds
- How it works:
- For numbers where the digits add up to less than 10:
- Example: 23 × 11 → 2 (2+3) 3 → 253.
- For numbers where the digits add up to 10 or more:
- Example: 57 × 11 → 5 (5+7) 7 → 5 (12) 7 → 627 (carry the 1).
- Why it’s cool: No calculator needed—just mental math!
Trick #2: Squaring Numbers Ending in 5
- How it works:
- Take the first digit, multiply it by itself +1, then tack on "25."
- Example: 75² → (7 × 8) = 56 → 5625.
- Pro tip: Works for any number ending in 5, no matter how big!
Trick #3: The 6-7-8-9 Finger Multiplication Hack
- How it works:
- Assign each finger a number (6-10). Touch the fingers you’re multiplying, count the touching and below fingers for tens, and multiply the above fingers for ones.
- Example: 7 × 8 → 5 (touching + below) and 3 × 2 (above) → 56.
- Bonus: Perfect for kids (or adults who never memorized times tables).
...plus 7 more tricks, including:
- The "Butterfly Method" for adding fractions.
- The "Russian Peasant" multiplication hack.
- How to calculate percentages in your head.
Math class should have taught you this stuff.