prozzy

the answer is -$97 for sure.
1 U, b% y2 B  v9 U- itvb now,tvbnow,bttvbThink about it this way
: U6 f" w& c" p/ A; T7 \( {' i1) if the 100 bucks is not a fake one, the store owner will gain $3 ($21-$18)
8 s; p& {0 Y% h& K5 L5 e# Y- B2) 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