Percentage Tricks
Finding 10% of a Number – Shift the Decimal Point
Ten percent is one tenth, so finding it is just a decimal-point shift.
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 find 10% of a number, simply move the decimal point one place to the left.
Why it works
Why It Works: “Percent” literally means “per hundred,” so 10% means 10 parts out of every 100 — which simplifies to exactly one-tenth. Dividing by 10 in our number system is the same as sliding every digit one place to the right, which is exactly why moving the decimal point does the job.
Formal Proof (for advanced learners)
10% = 10÷100 = 1÷10. Dividing any number n by 10 shifts its decimal representation one place value to the right, i.e. n÷10 is n with the decimal point moved one place to the left.
Examples
- 10% of 250 = 25.
- 10% of 84 = 8.4.
- 10% of 1500 = 150.
Step by step
Example A: Find 10% of 960
- Move the decimal point in 960 one place to the left: 96.
- So 10% of 960 is 96.
Example B: Find 10% of 45
- Move the decimal point in 45 one place to the left: 4.5.
- So 10% of 45 is 4.5.
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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Find 10% of 50.
Show answer
5. Move the decimal point in 50 one place to the left: 5. So 10% of 50 is 5.
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Find 10% of 380.
Show answer
38. Move the decimal point in 380 one place to the left: 38. So 10% of 380 is 38.
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Find 10% of 72.
Show answer
7.2. Move the decimal point in 72 one place to the left: 7.2. So 10% of 72 is 7.2.
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Find 10% of 1250.
Show answer
125. Move the decimal point in 1250 one place to the left: 125. So 10% of 1250 is 125.
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A game costs 640 coins and has 10% off. How many coins is the discount?
Show answer
64. Move the decimal point in 640 one place to the left: 64. So 10% of 640 is 64.
Tips and watch-outs
- A whole number has its decimal point at the end: 84 is 84.0, so 10% is 8.4.
- Use 10% as a building block: 5% is half of it, 20% is double, 30% is triple.