What is that one trick where....?

Question

you telll some1 to think of a number and then you tell them to add and subtract then when say your number 100?

it works everytime!

how do they do it?

i think you have to add and subtract a certain amount of times but how many?

Answer 1

Here are some websites that show you how to guess the number that a person is thinking of...otherwise the first guy is right

http://www.math.hmc.edu/funfacts/ffiles/...

http://www-prod.pen.k12.va.us/Div/Winche...

Answer 2

There are several tricks.  One is to take the original number, add 50, multiply by 2, and subtract double the original number.  So if their original number is x, you get:

(x + 50) * 2 - 2*x

=2x + 100 - 2x

=100.

You can throw in some other steps for show, but the trick is to make sure all the x's cancel out when you're done.