Introduction: Multiply or Divide Any Number by 5 Fast

So multiplying by 5 may seem easier than multiplying by 7 especially if you know the times tables but it's about to get a lot easier.

Step 1: Multiplying

Here are three numbers multiply them by 5 as fast as you can
52
68
47
Okay you have ten seconds no googling or using a calculator
If you can't get it here's how to do it.

Divide the number by two.
26
34
23.5

Now multiply by ten.
260
340
235

Easier right? It's okay if you don't get it at first it might take some practice especially with numbers that can't be evenly split.

Step 2: Dividing

Here are three number you think I'm crazy there's no way you can divide these in your head right? Wrong!
16
4
57

First double them.
32
8
114

Next divide by ten.
3.2
0.8
11.4

See this is something you can do with only your brain power!

Step 3: Base Ten

The number ten is a powerful number multiplying and dividing by it are much easier use this to your advantage..
Thanks for reading I hope to add more tutorials soon to find them look here:

https://www.instructables.com/member/mathcx

Comments

author
Zep25 (author)2016-10-15

Bye the way, 5x52 is 260 but good trick anyway.

author
Mathcx (author)Zep252016-10-20

I'm not sure if your trying to say it doesn't work for 52 but half of 52 is 26

Multiply by ten it's 260

author
Zep25 (author)Mathcx2016-10-20

Yes. Maybe I'm missing something... but your very first number in the example
is 52. Step #2 says divide by 2.
Which would be 26. You have it as 27. Then you multiplied by 10 giving you 270, which is incorrect. Your system works, you just divided incorrectly in the example.

author
Mathcx (author)Zep252016-10-22

how embarrassing I'll fix that. Sorry

author
DIY Hacks and How Tos (author)2016-10-15

This is a great trick. It always pays to be able to do math in your head.

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