Bunuel wrote:
Two pipes A and B can fill a tank in 8 hours. If only pipe A is open then it would take 4 hours longer to fill the tank. Find how much longer would it take if only pipe B is open.
A. 6 hours
B. 8 hours
C. 10 hours
D. 12 hours
E. 16 hours
Let’s let B = the number of hours it takes pipe B to fill the tank. We see that the combined rate of A and B is 1/8, and since pipe A can fill the tank in 8 + 4 = 12 hours, the rate of pipe A is 1/12 and the rate of pipe B is 1/B; thus:
1/12 + 1/B = 1/8
Multiplying by 24B, we have:
2B + 24 = 3B
B = 24
So it would take 24 - 8 = 16 hours longer if only B is open.
Answer: E
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