Thursday, October 07, 2010

Math Magic: Trick 1

You can surprise anyone by showing how quickly you can calculate whether one number is divisible by 3 or not.

Say 1235678. How you know if it is divisible by 3?

Add all the individual digits of the given number.

That is: (1+2+3+5+6+7+8)=32.

32 is not Divisible by 3.  Hence, the given number is not divisible by 3.

If a number is divisible by 3, the sum of all of its individual digits will also be divisible by 3.

Now let's take this number: 17746404.

Add them up:

(1+7+7+4+6+4+0+4)=33.

33/3=11.

So 17746404 is divisible by 3.

Now it's time for you to surprise someone.


Update:

My friend Anshul pointed out the trick is also applicable for 9. Thanks to him. 

1 comment:

Anshul said...

Same goes for 9.