Explanation:-
Solution:
P can fill cistern in 12 minutes
P fills cistern in 1 minute =
112112
112
Q can fill cistern in 15 minutes
Q fills cistern in 1 minute =
115115
115 part
P and Q together can fill cistern in 1 minute,
=112+115⇒960=112+115⇒960
=112+115⇒960 part
So, they can together fill cistern in 3 minute,
=3×960⇒920=3×960⇒920
=3×960⇒920 part
Rest Cistern =
1−9201−920
1−920 =
11201120
1120 part
11201120
1120 part cistern must be filled by Q in
1120115=8141120115=814
1120115=814 minutes
Alternatively,
Pipe P can fill cistern in one minute =
1001210012
10012 = 8.33%
Pipe Q can fill cistern in one minute =
1001510015
10015 = 6.66%
(P + Q) together can fill the cistern in one minute = 15%;
In 3 minutes cistern is filled = 45%
P become off, then rest of cistern will be filled by Pipe Q in =
556.66556.66
556.66 =
814814
814 minutes.
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