Math puzzles for adults: number challenges that make you think
A math puzzle for adults is a small constraint problem: you have a few numbers, a legal set of moves, and a target. You are not being asked to recall a chapter. You are being asked to search a short space of combinations until the constraints all hold.
Published 2026-10-27
Reasoning, not a worksheet
School exercises usually tell you the operation. A puzzle hides which operation is worth trying. The skill is keeping the target in view while you spend the numbers you are allowed to use, each once if the puzzle says so.
There is evidence that training the approximate number system can improve symbolic maths in adults, which is a near kind of transfer: number practice helping number work. It is not evidence that a puzzle app raises IQ or speeds up unrelated parts of your job.
Original challenges
Each puzzle uses only the numbers printed in it.
Easy
Using 2, 3, 4, and 5 exactly once, make 20 with ordinary arithmetic.
Answer and reasoning
Answer. (5 × 4) × (3 − 2) = 20
5 × 4 is 20, and 3 − 2 is 1. Multiplying by 1 spends the remaining numbers without changing the total.
Easy
The product of two whole numbers is 36 and their sum is 13. What are they?
Answer and reasoning
Answer. 4 and 9
Factor pairs of 36: 1 and 36, 2 and 18, 3 and 12, 4 and 9, 6 and 6. Only 4 + 9 = 13.
Medium
Three scores are whole numbers from 1 to 12. They add to 27. One score is double another. In order, the middle score is odd. What are the three scores?
Answer and reasoning
Answer. 6, 9, and 12
Doubles that leave a third score inside the cap: 5 and 10 (third is 12) or 6 and 12 (third is 9). Ordered, 5, 10, 12 has an even middle. Ordered, 6, 9, 12 has an odd middle.
Medium
Replace the box: 8 × box + 6 = 4 × box + 22.
Answer and reasoning
Answer. 4
8b + 6 = 4b + 22, so 4b = 16, so b = 4. Check: 32 + 6 = 38 and 16 + 22 = 38.
Harder
You may press +5 or ×2, starting from 1. Reach exactly 23. What is one shortest sequence of presses?
Answer and reasoning
Answer. ×2, ×2, +5, ×2, +5. Five presses.
Work backwards from 23. The last press was +5, from 18. 18 is ×2 from 9. 9 is +5 from 4. 4 is ×2 from 2. 2 is ×2 from 1. Forwards, the totals are 2, 4, 9, 18, 23.
How this relates to a scored round
Two5’s Numbers ideas include a target-number round: you are given operations and asked to hit a target. That is the same family as the puzzles above. It is not available to play on this site today. The point of publishing the method here is so you can practise the search, not so we can pretend a round is live.
Sources
On Two5
If you want target-number and sequence rounds with a score you can compare to your last attempt, join the Two5 waitlist. We will not pretend those rounds are open before they are.