Mental Math · Level Up · L4
Percents are built from easy building blocks. 10% is just ÷10, 5% is half of that, 1% is ÷100. Find a friendly block and scale it — 15% of 240 is 10% (24) plus 5% (12) = 36.
Watch the method
15% of 240: 5% of 240 is 240 ÷ 20 = 12. 15% is three of those, so 12 × 3 = 36.
5% of 240 is 240 ÷ 20.
15% is 3 lots of 5%.
Your turn
Use the method, then check. Stuck? Reveal the steps.
10% of a number is that number ÷ 10. 5% is half of 10%. 1% is ÷ 100. Any 'nice' percent is a few blocks added: 35% = 10%+10%+10%+5%.
Why it works
Percent means 'per hundred' — slice the number into hundredths, then take as many as you need.
10% of 480
÷10
480 ÷ 10 = 48.
15% of 240
10%
240 ÷ 10 = 24.
5%
half of 24 = 12.
Add
24 + 12 = 36.
35% of 280
10%
28, so 30% = 84.
5%
half of 28 = 14.
Add
84 + 14 = 98.
Thinking 10% means ÷ 100.
10% = ÷ 10. It's 1% that means ÷ 100.
Forgetting to scale the block.
Finding 5% isn't the answer for 15% — you need three of them.
12 problems across three tiers. Auto-graded on submit. Hints and a full walkthrough on every question. Your work is saved on this device — sign in to keep it across devices.
t₁ = 5, d = 3 and t1=5,d=3 both count. For a list of numbers, separate them with commas (e.g. 3, 10, 17).15% of 240 = ?
20% of 300 = ?
25% of 160 = ?
10% of 480 = ?
30% of 220 = ?
40% of 200 = ?
45% of 200 = ?
5% of 360 = ?
35% of 280 = ?
50% of 460 = ?
15% of 320 = ?
25% of 440 = ?