1 answer
(click or scroll down)
look at the money spent at each shop, starting with x
1: x/2 + 10, leaving x/2 - 10
2: x/4 - 5 + 10, leaving x/4 - 15
3: x/8 - 15/2 + 10, leaving 0
So, x = 7x/8 + 30 -5 - 15/2
x = 140
check:
at shop 1, spent 80, leaving 60
at shop2, spent 40, leaving 20
at shop 3, spent 20, leaving 0