FILE No.61Unsolved
Three guests ate at a restaurant. The bill was $25, but at the register the three each handed over $10, $30 in total.
The manager told the waiter, "The bill is $25, so give back $5." The waiter pocketed $2 of the $5 and returned $1 to each guest, $3 in total.
Each guest has now paid $10 - $1 = $9, so $27 in total. The waiter kept $2. $27 + $2 = $29. That is one dollar short of the original $30.
Did a dollar really disappear? Where did it go?
If you get stuck, open the hints one at a time, in order.
What is the $27 made up of?
Is the waiter's $2 already inside that $27?
Write out where each of the $30 went.
Did a dollar really disappear? Where did it go?
Choose the answer closest to the truth.
Adding the $2 to $27 is the mistake; nothing actually vanished
The answer is: adding the $2 to $27 is the mistake; nothing actually vanished.
The $27 paid by the guests consists of the $25 bill and the $2 kept by the waiter. The waiter's $2 is already included in the $27, so adding it again is double-counting.
The correct check: $27 - $2 = $25 (the bill). Or: $25 (bill) + $2 (waiter) + $3 (returned to guests) = $30, exactly the original amount.
The equation "$27 + $2 = $29" looks reasonable at first, but it counts the waiter's $2 twice.
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