Question

Manoj and Tamar are arguing about how a number trick they heard goes. Tamar tells their friend Andrew to think of a number, multiply it by five, and subtract three from the result. Then Manoj tells Andrew to think of a number, add five, and multiply the result by three. Andrew says that whichever way he does the trick he gets the same answer. What was Andrew's number? Justify your answer.

Answer 1

X - Andrew`s number;
x * 5 - 3 = ( x + 5 ) * 3
5 x - 3 = 3 x + 15
5 x - 3 x = 15 + 3
2 x = 18
x = 18 : 2
x = 9
Andrew`s number is 9.
Justify:
9 - 5 - 3 = 45 - 3 = 42
( 9 + 5 ) * 3 = 14 * 3 = 42