Let x be the amount in dollars that each of the 20 children were going to contribute; then 20x represents the cost of the present.

When 4 children dropped out, the remaining 16 each had to pay (x + 1.50) dollars. So, 16(x + 1.5) = 20x ⇒ 16x + 24 = 20x ⇒ 24 = 4x ⇒ x = 6, and so the cost of the present was 20 × 6 = 120 dollars.

Alternative Solution.

Since each of the 16 remaining children had to pay an extra $1.50, the extra payments totaled 16 × $1.50 = $24. This is the amount that would have been paid by the 4 children who dropped out, so each of the 4 would have paid $6. The cost of the gift was 20 × $6 = $120.

Twenty children were sharing equally the cost of a present for their teacher. When 4 of the children decided not to contribute, each of the other children had to pay $1.50 more. How much did the present cost, in dollars? ​

A. 50 ​

B. 80 ​

C. 100 ​

D. 120 ​

E. 150