Ask your friend to think of a random number, and don't let him tell it you. The following steps can be done in mind or on a calculator but be sure to press = after each step.
Step 1. + 3
Step 2. x 6
Step 3. - 9
Step 4. / 3 ( divide by three )
Step 5. - 3
Let him tell you the final result. Just quick divide it by 2 in mind, and you'll get the number your friend started out with. He'll be surprised when you tell him it! :-) ( the number)
The trick is, that when your friend multiply and divide, he not only divide the random number, but also the numbers you asked him to add. Math explanation follows. We'll call the random number R.
Step 1. R + 3
Step 2. 6(R + 3) = 6R + 18
Step 3. 6R + 18 - 9 = 6R + 9
Step 4. (6R + 9) / 3 = 2R + 3
Step 5. 2R + 3 - 3 = 2R
Interested in math or not, it works! :)
- 1.0 (Calculator)