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Mentally Multiply by 5, 50, 500, 5000
Posted 08-15-2009 at 12:15 PM by shabbir
To quickly multiply by 5, divide the number in two and then multiply it by 10. This can be done quickly in your head.
How it works.
We can write 5 as 1/2x10
So now lets say we would like to multiply 28 and 5 and so using the above formula we can
First half 28 i.e. 14
Now multiplying it to 10 gives 140 and so answer is 140.
The same thing can be applied to 50 which is half of 100 i.e. 1/2x100
Generalizing the above logic we can apply it to 500, 5000 ...
How it works.
We can write 5 as 1/2x10
So now lets say we would like to multiply 28 and 5 and so using the above formula we can
First half 28 i.e. 14
Now multiplying it to 10 gives 140 and so answer is 140.
The same thing can be applied to 50 which is half of 100 i.e. 1/2x100
Generalizing the above logic we can apply it to 500, 5000 ...
Total Comments 2
Comments
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mm..nice method...
Posted 08-15-2009 at 05:43 PM by priyad
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Thanks
Posted 08-16-2009 at 09:59 AM by shabbir
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