the answer is -$97 for sure. & R0 q5 t$ q5 {! ^公仔箱論壇Think about it this way 5.39.217.776 j# X0 q9 X# {8 ^9 M/ `# M
1) if the 100 bucks is not a fake one, the store owner will gain $3 ($21-$18) 9 R' u! I: ?# L% G) C公仔箱論壇2) Now, the owner discovered that the 100 bucks is fake. You can think this as a lost of $100. therefore the overall gain is $3-$100 = -$97