doing mathFree tools

Know the equivalents: a mental math trick

When to use it: A percent is a simple fraction, or a fraction is a simple percent.

Worked example

25% of 360 as 1/4A bar for 360 cut into 4 equal parts. 25% is 1/4, one part: 90.3601/4901/4901/4901/490360 ÷ 4 = 90
  1. Learn the anchors: 1/2 = 50%, 1/4 = 25%, 3/4 = 75%, 1/5 = 20%, 1/10 = 10%.
  2. Eighths are half of quarters: 1/8 = 12.5%.
  3. 1/3 and 2/3 never end: 1/3 ≈ 33.3% and 2/3 ≈ 66.7%.

example 25% of 360

  1. 25% is 1/4.
  2. 360 ÷ 4 = 90.

Answer: 90

Try three

  1. 25% of 80

    Show the answer

    20

  2. 12.5% of 136

    Show the answer

    17

  3. 75% of 68

    Show the answer

    51

Practice this in the app →

Or start with 4 warm-up problems, no sign-up →

Used in: Fraction basics · Percents · Division

More mental math tricks

This technique and its worked example are Doing Math’s own lesson text, checked by a blind re-solve and a review on September 27, 2026.