X% of Y

Build any percent from 10%, 5% and 1%.

Commission, discounts, budget splits, "what’s 15% of our pipeline?" This is the most common math in business, and it only takes one idea.

The move

10% = move the decimal one place left. Build everything else from that: 20% is double it, 5% is half of it, 15% is 10% + 5%. And a secret: x% of y = y% of x, so 8% of 50 is the same as 50% of 8, which is 4.

Worked example

15% of 340

  1. 10% of 340 = 34
  2. 5% is half of that = 17
  3. 15% = 34 + 17 = 51
  • "Percent" literally means "per hundred". 7% is 7 out of every 100.
  • Use the swap trick when one number is friendly: 4% of 25 = 25% of 4 = 1.