Always Get the Number 15 Trick
Here is another cool simple trick that will always get the number 15.

Think of any number.
Example 45786

Multiply that number by 3
45786 x 3 = 137358

Now add 45 to the answer
137358 + 45 = 137403

Multiply the result by 2
137403 x 2 = 274806

Divide that new answer by 6
274806 / 6 = 45801

By subtracting this answer with your original answer will give you the number 15.