Multiply or Divide Any Number by 5 Fast

1,083

17

5

Intro: 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

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    5 Discussions

    0
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    Zep25

    2 years ago

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

    3 replies
    0
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    MathcxZep25

    Reply 1 year ago

    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

    0
    None
    Zep25Mathcx

    Reply 1 year ago

    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.

    0
    None
    MathcxZep25

    Reply 1 year ago

    how embarrassing I'll fix that. Sorry

    0
    None

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