# 25 Easy Arithmetic Tricks You Can Start Using Right Now

Math is seen as the realm of logic and rationality, but even so there is a lot of trickiness in the number world! From quick ways to do arithmetic to various statistical anomalies, these are 25 Easy Arithmetic Tricks You Can Start Using Right Now!

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## Multiply by 5

To do this quickly, divide by 2 and then multiply by 10

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## Multiply by 4

This may seem obvious but to do this in your head, just double twice. Some people do this intuitively and others don’t.

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## Hailstone numbers

Start with a random number. If it is even then divide by 2. If it is odd, multiply by 3 and add 1. If you keep going you will find that no matter where you started you will eventually hit 1. Like hailstones, the number will go up, and inevitably come back down. This is an example with 7:

7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1

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## Multiple of 3

Your math teacher may never have told you this but you can check if a number is a multiple of 3 simply by checking whether the sum of its digits is a multiple of 3.

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## You can't just put 10% back

If your boss ever tells you that he is going to cut your salary by 10% but let you work 10% more to make up for it, don’t do it! Let’s say you made \$10 per hour. 10% off would be \$9 per hour. Adding 10% back would be \$9.90. Be careful what the percentage refers to!

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