This is a very interesting trick. We used this trick so many times in my school days that I still remember it. Let’s take a look.

1. Ask the user to think of any number silently in his mind (suppose it is 50).
2. Tell him his friend has the same number, so he should add them together. (Now it is 50 + 50 = 100)
3. Give him your number (Say 150) and tell him to add it in the total (100 + 150 = 250)
4. Tell him to divide the total by 2 (250/2 = 125)
5. Tell him to give his friend’s number back to him. (125 – 50 = 75). Tell him to remember this total in his mind.
6. Now, if you divide your number (i.e. 150) by 2, you’ll get his final number (e.g. 150/2 = 75). Simply announce your answer which is equal to user’s answer and watch the shocked look on his face.

The key part of this trick is “your number” and “dividing” it by ,“2”. Thus regardless of the user number the answer is always with you.

So whatever the user thinks, the final result will always be the half of “your number”. For e.g. If you give 100 to add to the total, then the final answer will be 100/2 = 50.