Type the answer and press Enter. All answers are whole numbers. How many can you solve before time runs out?
%
—
Time
0
Solved
—
Accuracy
Mental percentage tricks
Nearly every percentage can be built from a few anchors. 10% is just the decimal shifted (10% of 340 = 34); 5% is half of that; 1% is two shifts. 25% is a quarter, 75% is three quarters. And the reversal trick often saves you: x% of y always equals y% of x, so 4% of 50 becomes 50% of 4 = 2. For “A is what % of B”, divide and scale: 30 of 120 → 30/120 = 1/4 = 25%. The quiz rotates all three question types so the anchors become automatic.
Frequently asked questions
What's the fastest way to compute a percentage in my head?
Anchor on 10% (shift the decimal) and build from there: 5% is half of 10%, 20% is double, 1% is two shifts. For 15% of 60: 10% is 6, 5% is 3, total 9. With the anchors automatic, most everyday percentages take a second or two.
What is the percentage reversal trick?
x% of y always equals y% of x, because both are x·y/100. So an awkward 4% of 75 becomes an easy 75% of 4 = 3, and 16% of 25 becomes 25% of 16 = 4. Whenever one direction feels hard, flip it.
Why do the questions only use 5, 10, 20, 25, 50 and 75 percent?
Those are the anchors real life uses most — tips, discounts, sales tax estimates — and they guarantee whole-number answers so you can focus on speed. Once they're automatic, odd percentages become combinations of them (e.g. 35% = 25% + 10%).