Awoman walks in and steals 100 from a register. 5 minutes later uses the same 100 to buy merchandise from that same store and buys 70 worth of merchandise with that same 100. he gives her 30 in change. how much did the store lose

She took 100, the store has       - 100
she went back and bough
70 bucks in stuff, the store has - 70

yes, she took the $100 bill and gave it, got back $30, that means she only kept $30 from the original bill.

the store however, lost the original $100 bill plus the $70 in merchandise, so they have -$170.