Subtraction Within 20 Game
Take a single-digit number away from a teen number, such as 15 − 7. Every question crosses back below ten.
Type answers on your keyboard, or tap the number pad.
Time 60Correct 0
Practise these again:
How to play
- Choose the 60-second challenge or untimed practice, then press Start.
- Type each answer on your keyboard or tap the number pad. It’s checked as soon as you’ve typed enough digits, or press ✓.
- Get one wrong and you’ll see the right answer, and the question comes back a little later.
- At the end, check your score and the facts to practise again.
What it practises
- Subtraction facts within 20
- Subtracting across ten
- Using addition facts to subtract
Level: Grades 1–2 (ages 6–8)
Tips for subtracting within 20
Go back to ten first: 15 − 7 = 15 − 5 − 2 = 8.
Count up to ten and on: for 13 − 9, count 9 → 10 (1) → 13 (3), so the answer is 4.
Questions and answers
What does “subtracting across ten” mean?
It means the answer ends up below 10 even though you started above it, as in 14 − 6 = 8. Stopping at 10 on the way (14 − 4 − 2) makes it easier.
Which facts cause the most trouble?
Facts like 13 − 8, 15 − 7 and 17 − 9 usually cause the most trouble, because they take away more than the ones digit.
Is there a game for smaller numbers?
Yes. Subtraction Within 10 covers the basic facts, and it’s a good place to start before this game.