7) Every month, a wholesaler sends a retailer 24 liters, 32 liters, and 40 liters of three different varieties of wine using the minimum number of identical and fully filled containers, of course without mixing different qualities of wine in the same container. How many containers will the retailer receive in a year?
(A) 36
(B) 72
(C) 144
(D) 288
(E) the data is insufficient.
7) The answer is (C)

Since the containers must all be the same, their capacity in liters must be a divisor of 24, 32, and 40, and therefore cannot exceed the greatest common divisor of these numbers, which is 8. The minimum number of containers is obtained when their capacity is the maximum possible, and therefore equal to 8 liters. Using containers of 8 liters, the wholesaler will use $3+4+5=12$ containers per month, and therefore the retailer will receive $12 \times 12=144$ containers in a year.