The extra dollar. The cost of dinner for two people is $45 and they both give the waiter $25 each. Of

the extra $5 the waiter is allowed to keep $3 as a tip and returns $1 to each person. So the two people
paid $24 each, making a total of $48 , and the waiter has $3 . The total is therefore $48 + $3 = $51.
Where did the extra $1 come from?

The extra $1 is a result of a mathematical error. The total cost of dinner for two people is $45, and the amount they both gave to the waiter is $50 ($25 each). When the waiter returns $1 to each person, the amount they have spent on dinner is reduced by $2 ($1 each), making the total cost of dinner $47 ($45 + $2). Adding the $3 tip the waiter kept, the total amount is $50, not $51. There is no missing dollar; it's just a misunderstanding of the math.