A man goes into a store and says to the owner: "Give me as much money as I have with me and I will spend $10."
It is done and the man repeats the operation at a second and a third store, after which he has no money left.
How much did he start with?
1. Let x be how much he started with.
How Much He Had Left in Store 1: x+x-10
How Much He Had Left in Store 2: (2x-10)+(2x-10)-10=2x+2x-10-10-10=4x-30
How Much He Had Left in Store 3: (4x-30)+(4x-30)-10=4x+4x-30-30-10=8x-70
2. It's implied that 8x-70=0, so 8x must equal 70 after adding 70 on both sides of the equation.
3. Divide 8 on both sides of the equation and we get x=70/8, or x=$8.75.
Answer: The man started with $8.75.