Working backward

Question

Brad went to store A and spent 1/2 of his money. He then went to store B and spent 1/2 of his money. He went to store C and spent 1/2 of his money. Now he has 1Php left. How much money did he have at the start?

Answer 1

Let's assume he had amount M. Solving the following equation will give the answer:

 

(M/2)/2 = 1, or

 

M=4 (the answer)