prozzy

the answer is -$97 for sure.
, ~9 F" ?, [7 W公仔箱論壇Think about it this way
: Z4 }2 Y- T4 b9 }% c1) if the 100 bucks is not a fake one, the store owner will gain $3 ($21-$18)
5 `# G3 e5 \% p6 b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