A neat number trick

I was recently shown a number trick that works on any number with 3 or more digits. I will show you an example with a 5 digit number.

Ask someone to write down a 5 digit number, make sure they don't show you.

e.g. 59716

Now ask them to add up all the digits to make a new number.

e.g. 5 + 9 + 7 + 1 + 6 = 28

Now take this new number away from the original

e.g. 59716 - 28 = 59688

Now ask them to strike out at random one of the digits in the new number. Once they have done that ask them what the remaining 4 are and mentally add them together

e.g. Strike out the number 5 and then add together 9 + 6 + 8 + 8 = 31

Now using the nine times table find the next multiple of 9 above 31. In this case it is 36. Subtracting 31 from 36 gives you 5 and that tells you the number that was randomly removed.

I could have struck out 6, then added the remaining digits together to get 30. Then, once again subtracted 30 from 36 and got the number 6.

As I said, it works on any number with 3 or more digits, but be careful if your addition of the remaining numbers equals a multiple of nine because you have to take it from the next multiple up. For example you subtract 9 from 18, not 9 from 9.