Mental Math Trainer — Percentages, Fractions, Squares

Friendly, private practice. No accounts. Press Enter to submit, Esc to skip.

Mode: Practice
Time: —
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Tips

  • Press Enter to submit, Esc to skip.
  • Decimals allow a small rounding tolerance (±0.01).
  • Use “Daily Seed” to get a repeatable set for the day.

FAQ

What shows up in each topic?

Percentages: “What is a% of b?” (clean numbers on Easy).
Fractions: “What is a/b of n?” (chosen to land on integers by default).
Squares: “n2 = ?” (range grows with difficulty).

Is my data uploaded?

No. The trainer runs entirely in your browser. Bests and settings are stored locally.

5 Fun Facts about Mental Math

10% trick is instant

Sliding a decimal left is a built‑in shortcut: 10% of any number is just “shift left”. From there, 5% is half of that, and 1% is one more shift.

Percent hack

Abacus users beat stopwatches

Competitive “mental” mathletes often visualise an imaginary abacus (soroban). World champions add or multiply 15+ numbers in under 10 seconds using that mental image.

Soroban mind

Squares carry a pattern

Consecutive squares differ by odd numbers: n² − (n−1)² = 2n−1. Memorising a few anchors lets you jump to nearby squares faster.

Pattern hop

Cross-multiply to sanity-check

For fractions of a whole, a quick cross-multiply check (a×n vs. b×answer) flags slips immediately—handy under a timer when digits blur.

Error catch

Break numbers into friends

Humans add fastest in chunks: 17% of 240? Take 10% (24), 5% (12), 2% (4.8) → 40.8. Decomposing beats long multiplication every time.

Chunking

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