We’ll go through an example, where your friend secretly picks the number 4. This trick works with any number, but keeping it between 1 and 20 makes it less likely that your friend will make a mistake.
For example, if she chose 4, her new number is 4 + 1 = 5.
5 x 2 = 10.
10 + 4 = 14.
14 ÷ 2 = 7.
7 - 4 = 3.
This trick won’t be too impressive with close friends or classmates, since you probably already know their age. Pick someone at least 10 years old and no more than 99 years old.
For example, if he is 32 years old, he should take the 3 and multiply it by 5. The answer is 3 x 5 = 15.
In our example, he would silently add 15 + 4 = 19.
19 x 2 = 38.
Since the subject of our example is 32 years old, he would add 2 to his last answer. His last answer was 38, so he calculates 38 + 2 = 40.
In our example, 40 - 8 = 32.
Instead of adding 4 and later (secretly) subtracting 8, you can add 3 and subtract 6, or add 2 and subtract 4, or even add 25 and subtract 50. Just remember you’ll need to subtract twice as much as the original number, because it got doubled in one of the later steps. To really switch it up, try this: double your age, add 2, multiply by 5, and subtract 10. You need both the doubling and multiplication by five to move the first digit of his age (3 in our example) to the tens place where it belongs (3 x 2 x 5 = 30).
For example, he could write 222.
For example, 2 + 2 + 2 = 6.
222 / 6 = 37,
