hi]

two pipes a and b can seperately fill a tank in 20 mins and 30 mins respectively, which a third pipe C can empty the full tank iin 15 mins

If all pipes are opened together then in what time is the empty tank filled?

bye

gautam93

Printable View

- Sep 16th 2006, 01:01 AMgautam93help me anyone
hi]

two pipes a and b can seperately fill a tank in 20 mins and 30 mins respectively, which a third pipe C can empty the full tank iin 15 mins

If all pipes are opened together then in what time is the empty tank filled?

bye

gautam93 - Sep 16th 2006, 01:28 AMCaptainBlack
The first pipe fills the tank at a rate of 1/20 of a tank/min

The second pipe fills the tank at a rate of 1/30 of a tank/min

The third pipe empties the tank at a rate of 1/15 of a tank/min.

Starting from empty the content of the tank at time t is:

t(1/20+1/30-1/15).

The solution is the time t for which:

t(1/20+1/30-1/15)=1,

which is 60 minutes.

RonL - Sep 16th 2006, 05:02 PMThePerfectHacker
Here is a useful rule I develpoed that seems to help people.

If it takes 'a' units of time to do a job and 'b' units of time to do the same job by two different things or people then it takes (ab)/(a+b) to do it together. - Sep 17th 2006, 12:51 AMCaptainBlack
Your rule does not lead to understanding, while the reason for it does.

Though it seems to be the fashion of the day, I would discourage

learning rules at the expense of understanding. I normally work many

things, others seem to use rules for, from more primitive principles.

RonL