Question

One pump can drain a pool in 7 minutes. When a second pump is also used, the pool only takes 5 minutes to drain. How long would it take the second pump to drain the pool if it were the only pump in use? Round your answer to the nearest tenth.
a) 33.0 minutes
b) 2.9 minutes
c) 17.5 minutes
d) 24.1 minutes

Answer 1

please someone help me :(

Answer 2

The answer is (c).

Answer 3

how is it c?

Answer 4

See:
A can drain 1/7 of the pool in a minute.
A and B can drain 1/5 of the pool in a minute.
B can drain 1/7 - 1/5 of the pool in a minute
Thus B can drain 2/35 of the pool in a minute.
35/2 is 17.5 minutes.
Hence the answer is (c).