How to Find a Percentage of a Quantity Mentally

Updated Sep 14, 2026 · View standard page

To find 15% of 240 mentally, split 15% into 10% and 5%.

10% of 240 = 24
5% of 240 = 12

So:

15% of 240 = 24 + 12 = 36

Another example

Find 19% of 300 by using 20% and 1%.

20% of 300 = 60
1% of 300 = 3
19% = 60 − 3 = 57 Useful benchmarks: 50% is half, 25% is a quarter, 10% is divide by 10, and 1% is divide by 100.