Fastest Method to Multiply and Divide with 5

Multiplication and Division by 5 in the normal way can be easy. But there is a much easier way of doing it. This works best when you don't have a book and a pen beside you.

Multiplication by 5

Eg 1: 18 x 5
What we should do is add a zero to the right of 18 making it 180 and divide this number by 2 which gives the answer 90.
Easy??

Eg 2: 28 x 5
We write a zero to the right of 28 and it becomes 280. Divide by two. The answer is 140.

Theory behind the trick:
The theory behind this trick is very simple. By adding a zero to the right of a number, what we are actually doing is multiplying the number by 10. Then we divide by 2.
Let 'n' be any number. When we do the two operations above,
we get 
n x 10/2 which is equal to n x 5.

Division by 5
This is the reverse process of the multiplication trick. For dividing by 5, we first multiply by two, then divide by 10.

Eg 1: 220/5
We first multiply 220 by 2 which gives 440 then remove the zero.
The answer is 44.

Eg 2: 125/5
Multiply 125 by 2. We get 250. Remove the zero. The answer is 25.

You might have doubt on what to do if there is no zero in the unit place to remove.
For example if the question is 142/5
we do the same step, 142 x 2 which is 284. This number can be also written as 284.0 . Now the decimal point will move one step to the left. The answer to 142/5 will be 28.4

This looks a longer process but after you practice using this method, you can get faster results because doubling, halving and adding zero are easier

If you have any doubts, don't hesitate to comment below..

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