>>4438826The money that a thief has at the start of the transaction is 0$.
Then we assume the amount of money that cashier has at the start plus stock is 100$+70$=170$
Now here comes to tricky bit we have the thief stealing some money, 100$ to be precise, then we now have
170$−100$=70$
Now we say that the thief buys 70$ worth of food, this is a zero sum transaction i.e. the transaction is balanced both ways so we have
70$−70$(food sold)+70$(money used to purchase food)=70$
Now that is what we have in left with the cashier.
Now compare with the start
70$−170$=−100$
Is what the cashier is down by.
Now the thief has
70$(food)+$30(change)=$100
Effectively $100.
