Home > Practice > Arithmetic Aptitude > Time and Work > Miscellaneous
1. Two pipes, P and Q can fill a cistern in 12 and 15 minutes respectively. Both are opened together, but at the end of 3 minutes, P is turned off. In how many more minutes will Q fill the cistern?

Solution:
P can fill cistern in 12 minutes
P fills cistern in 1 minute = 112
Q can fill cistern in 15 minutes
Q fills cistern in 1 minute = 115 part
P and Q together can fill cistern in 1 minute,
=112+115⇒960    part
So, they can together fill cistern in 3 minute,
=3×960⇒920    part
Rest Cistern = 1−920  = 1120  part
1120 part cistern must be filled by Q in
1120115=814   minutes

Alternatively,
Pipe P can fill cistern in one minute = 10012 = 8.33%
Pipe Q can fill cistern in one minute = 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 = 556.66 = 814 minutes.

You must login to add comments. Login now.