Multiplication Tricks
Multiplying by 9 – Times 10, Take Away One
Nine is one less than ten, so multiply by 10 and take the number away once.
This page explains the rule, shows why it works, and walks through worked examples. Then you can try it yourself and check your understanding with practice questions. Use the previous and next links at the bottom to move through the tricks in order.
The rule
The Rule: To multiply by 9, multiply by 10 and subtract the original number.
Why it works
Why It Works: 9 is just one small step below 10. Multiplying by 10 is instant — you simply add a zero — and since “9 groups of something” is the same as “10 groups, minus 1 group,” subtracting the original number once quietly corrects for that small overshoot from rounding up to 10.
Formal Proof (for advanced learners)
n × 9 = n × (10 − 1) = n×10 − n×1 = 10n − n, a direct application of the distributive law.
Examples
- 8 × 9 → 8 × 10 = 80, then 80 − 8 = 72.
- 23 × 9 → 230 − 23 = 207.
- 150 × 9 → 1500 − 150 = 1350.
Step by step
Example A: 83 × 9
- Multiply by 10: 83 × 10 = 830.
- Subtract the original number: 830 − 83 = 747.
Example B: 250 × 9
- Multiply by 10: 250 × 10 = 2500.
- Subtract the original number: 2500 − 250 = 2250.
Try it yourself
Now it is your turn. A new random question appears each time. Type your answer in the box and press Check Answer. If you are right, we show how the trick got you there, step by step. If you are not, you will see the full working two ways, the shortcut and the usual method, so you can spot exactly where your answer differed. Press New Question as often as you like: a few quick rounds is the best way to make the trick feel automatic.
Practice questions
Have a go on paper first, then tap Show answer to check your method.
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Work out 7 × 9.
Show answer
63. Multiply by 10: 7 × 10 = 70. Subtract the original number: 70 − 7 = 63.
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Work out 34 × 9.
Show answer
306. Multiply by 10: 34 × 10 = 340. Subtract the original number: 340 − 34 = 306.
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Work out 65 × 9.
Show answer
585. Multiply by 10: 65 × 10 = 650. Subtract the original number: 650 − 65 = 585.
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Work out 128 × 9.
Show answer
1152. Multiply by 10: 128 × 10 = 1280. Subtract the original number: 1280 − 128 = 1152.
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One game costs 9 coins. How many coins do 46 games cost?
Show answer
414. Multiply by 10: 46 × 10 = 460. Subtract the original number: 460 − 46 = 414.
Tips and watch-outs
- The digits of a single-digit × 9 answer always add up to 9: 9 × 7 = 63 and 6 + 3 = 9.
- The same idea works for 99: multiply by 100 and subtract the number once.