Twenty subtraction problems, all on the board at once, all built from numbers under 100. You'll see things like "82 − 47" — the kind of two-digit borrowing that's easy on paper and satisfying to nail purely in your head.
The larger number is always first, so every answer is a positive whole number; you never have to worry about negatives. The clock counts up from your first keystroke, so this works both as a relaxed practice board and as a time-attack against your own best run.
How to play
All 20 differences are shown at once — clear them in any order.
Type an answer in the box; an exact match with an unsolved problem commits instantly, no Enter required.
Wrong number + Enter = a quick shake and a cleared box. No lives lost, no score penalty.
The stopwatch starts when you start typing and runs until the board is clear or you give up.
After finishing, "Reveal answers" shows any problems you left unsolved.
What counts in this quiz
20 problems per run, regenerated every play-through.
The starting number is between 25 and 99; what's taken away is at least 10 and always smaller than the starting number.
Answers are unique across the board, so each number you type resolves to exactly one problem.
What's not included — and why
No negative answers — the generator always subtracts the smaller number from the larger, so results stay at 1 or above.
No decimals or fractions — whole numbers only.
Good to know
The − sign debuted in the same 1489 book as the + sign; merchants had been using both as warehouse marks for surplus and deficit.
European mathematicians distrusted negative numbers for centuries — well into the 1600s some called them "absurd numbers".
Cashiers historically subtracted by adding up — counting on from the price to the amount paid — which is why the technique is called "making change".