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 had php1 left. How much money did he have at the start?

Answer 1

You can also work forward:

 

Start with x.  Spend half of x, leaving x/2.  Then spend half of x/2, leaving x/4.  Then spend half of x/4, leaving x/8, which we are told is 1.

 

x/8 = 1

 

x = 8

Answer 2

As you say, working backwards:

Before C Brad had 2 php (what's a php?)

Before B Brad had 4 php

Before A brad had 8 php

 

Check

Before A 8, spend 4

Before B 4, spend 2

Before C 2, spend 1

One left over