Pipes and Cisterns Practice Test 3 with solutions

Question : 7 of 7

Marks: +1, -0

When the waste pipe is closed, two taps can separately fill a cistern in 10 and 12 minutes respectively. When the waste pipe is opened they together fill it in 15 minutes. How long does it take waste pipe to empty the cistern, when the taps are closed?

8 min. 34 sec.
7 min. 10 sec.
12 min.
10 min.

Validate

Solution:

The waste pipe can empty in 1 min. =

1/{10}+1/{12}-1/{15}

{11}/{60}-1/{15}

7/{60}

of the cistern.
Hence, the waste pipe can empty the cistern in

{60}/7

minutes, i.e., 8 minutes 34 sec. (approx)

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