Math Sprint: Spot the Wrong Equation in 60 Seconds ➗
Published: August 10, 2026 · 4 min read
Math Sprint throws equations at you and asks whether each is correct. Sixty seconds, as many as you can. The people who score well are not calculating faster — they're mostly not calculating at all.
The rules
An equation appears — 7 × 8 = 54. Tap true or false. Sixty seconds, speed and accuracy both count.
Rejecting without calculating
Three checks will resolve most equations in well under a second.
The last digit. 7 × 8 must end in 6, because 7 × 8 = 56 and the units digit of a product depends only on the units digits. So 7 × 8 = 54 is wrong on sight — no multiplication performed. This one check catches a large share of false equations.
Rough size. 47 × 21 is about 50 × 20, so about 1,000. An answer of 587 or 2,410 is out before you've looked at the digits.
Odd and even. Odd × odd is odd. Anything × even is even. Odd + odd is even. 13 × 17 = 220 dies immediately — two odds can't multiply to an even.
A fourth, if you like them: casting out nines. Add the digits of each side down to a single digit; if the two don't match, the equation is false. 123 × 4 = 492 → left is (1+2+3=6) × 4 = 24 → 6; right is 4+9+2 = 15 → 6. Consistent, so probably right. It never proves an equation correct, but it disproves a lot of them fast.
Why this is worth doing
Estimation and sanity-checking are more useful in real life than exact mental arithmetic, and they're what this game actually trains. Knowing instantly that a number is the wrong size is the skill that catches a misplaced decimal on an invoice.
We're not going to claim it makes you better at maths generally. It makes you quicker at deciding whether a number is plausible, which is a genuinely useful and much narrower thing.
About our version
Sixty-second rounds with difficulty that scales to your streak, covering all four operations. Scores stay on your device.
It runs in your browser, works offline once loaded, needs no account, and costs nothing.
Questions people actually ask
How do I check an equation quickly?
Check the last digit of a product, check the rough size, and check odd versus even. Between them they reject most wrong equations without any calculation at all.
What is casting out nines?
Sum the digits of each side down to one digit. If the two results differ, the equation is definitely false. If they match it's probably right — the check can disprove but not prove.
Keep reading
- Brain Training Games: Focus, Memory and Reaction 🧠 — A Schulte table, a Stroop test, a memory sequence, a reaction timer and mental arithmetic — five games built around a number you can try to beat tomorrow.
- Kakuro: The Cross-Sum Puzzle Worth Learning 🔢 — A crossword made of sums. Steeper than Sudoku, more satisfying, and the entire game opens up once you memorise about six number combinations.
- Scan 25: The Schulte Table, and How to Get Faster at It 👁️ — Twenty-five numbers, one grid, find them in order. The people who go fast aren't looking harder — they're looking less.
Play Math Sprint now
60-second rounds, all four operations, difficulty that follows your streak. Free.