Mental Subtraction Test
mediumSubtraction is where most mistakes happen in mental maths. This test asks ten questions per round: Easy subtracts 2-digit numbers, Medium subtracts 3-digit numbers, and Hard takes a 3-digit number from a 4-digit number.
3-digit minus 3-digit.
Three tricks do most of the work: count up to the bigger number, shift both numbers by the same amount, or round and adjust. The chart lists complements to 100 to speed up all three.
Complements to 100 (what to add to reach 100)
| Number | Complement | Number | Complement |
|---|---|---|---|
| 3 | 97 | 52 | 48 |
| 7 | 93 | 58 | 42 |
| 12 | 88 | 64 | 36 |
| 18 | 82 | 71 | 29 |
| 24 | 76 | 75 | 25 |
| 29 | 71 | 83 | 17 |
| 36 | 64 | 89 | 11 |
| 43 | 57 | 94 | 6 |
| 47 | 53 | 98 | 2 |
Tricks for faster mental subtraction
- Count up instead of taking away: for 1000 − 647, go 647 → 650 (3), then 650 → 1000 (350). The answer is 3 + 350 = 353.
- Add the same amount to both numbers: 73 − 38 becomes 75 − 40 = 35.
- Round and adjust: 603 − 298 = 603 − 300 + 2 = 305.
- Know your complements to 100 and 1000. 1000 − 647 is just the number that completes 647 to 1000.
Frequently asked questions
What is 1000 − 647?
1000 − 647 = 353. Count up instead of taking away: for 1000 − 647, go 647 → 650 (3), then 650 → 1000 (350). The answer is 3 + 350 = 353.
What is 73 − 38?
73 − 38 = 35. Add the same amount to both numbers: 73 − 38 becomes 75 − 40 = 35.
What is 603 − 298?
603 − 298 = 305. Round and adjust: 603 − 298 = 603 − 300 + 2 = 305.
How can I subtract faster in my head?
Count up instead of taking away: for 1000 − 647, go 647 → 650 (3), then 650 → 1000 (350). The answer is 3 + 350 = 353. Add the same amount to both numbers: 73 − 38 becomes 75 − 40 = 35.
How is the speed maths test scored?
Each test has 10 questions. Answer 8 or more correctly to pass. Your time is recorded for the whole test, and your best time for each test and level is saved on your own device, so you can try to beat it.