Machine A, operating alone at its constant rate, produces 500 feet of a particular fiber in 2 hours. Machine B, operating alone at its constant rate, produces 500 feet of the same fiber in 3 hours. Machine C, operating alone at its constant rate, produces 500 feet of the same fiber in 5 hours. How many hours will it take machines A, B, and C, operating together at their respective constant rates, to produce 1,000 feet of the fiber?
-
A$$\frac{60}{31}$$
-
B$$\frac{15}{7}$$
-
C$$\frac{25}{11}$$
-
D$$\frac{10}{3}$$
-
E$$\frac{20}{3}$$
显示答案
正确答案: A