On a trip, the fare was 75¢ for each adult and 50¢ for each child. If 20 passengers paid $12.00, how many adults and children went?

Which of the following equations could not be used to solve the problem?

A) 75x+50 (20-x) = 1200

B) 75 (20 - x) + 50x = 1200

C) 75x + 50x = 20 (1200)

There are two cases in which this question can be answered. In our first case, let the number of adults be x and that of the children, 20 - x. On the second case, we let x be the number of children and 20 - x for adults. In the first case, the total fare may be expressed as 50x + 75 (20 - x) = 1200 and 75x + 50 (20 - x) = 1200. The expression in the first case is in letter b and the second case in letter a. Therefore, the answer for this item is letter c.