Cistern

shashank.ism -

how would u reach to the ans by just taking average..would u elaborate ur answer in mathematical form..I am not getting your solution money...please elaborate...

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I wouldn't reach the answer by just taking the average... hence why it was an incorrect answer. the mathematical explanation IS that i took the average

money9111 wrote:shashank.ism -

how would u reach to the ans by just taking average..would u elaborate ur answer in mathematical form..I am not getting your solution money...please elaborate...

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I wouldn't reach the answer by just taking the average... hence why it was an incorrect answer. the mathematical explanation IS that i took the average

hmm.... i got it but averaging will not give you the answer for sure as you are averaging the time rather you should average work done to get to the answer.

harsh.champ wrote:Two taps can fill a cistern in 8 hours and 16 hours respectively and another 3rd tap can empty it in 12 hours.If all three are opened simultaneously,what proportion of the cistern is filled in 6 hours?

(A)1/2
(B)1/4
(C)5/6
(D)3/4
(E)5/8


Note:-Read the question very carefully.

Assuming that the Cistern was empty when you opened the taps (see I am careful)

First tap can fill 1/8 in one hour
second can fill 1/16 in one hour
third can empty 1/12 in one hour

if all were opened The tank will be (1/8+1/16 -1/12) = 1/4( 1/2-1/3+1/4) = 1/4(1/6+1/4) =5/48

if you open it for 6 hours 5/8 will be filled

E - careful again - I put spoilers

money9111 wrote:harsh.champ i just realized that the OA is not provided... it's clear what it is.. but can you post it anyway?

shashank.ism - i simply took the overall average...

Tha OA is E.

The important part in the question was that 3rd tap was emptying the vessel not filling it.
Thus the equation will be (1/8+1/16 -1/12) and not (1/8+1/16 +1/12).
So,the answer will be 5/8.
I guess it is clear now.

money9111 wrote:I was going to go that route but decided to just average them... clearly not the best option but now I know for next time... so basically for all rate problems add them together by finding the LCD and then reduce etc etc

Hey money9111,
The imp. part was that we have to subtract the rate by the 3rd tap so we cannot just average the three.
This can be a very important trap that u can face in the test.I guess working through the "Word Translations" will further help you to point out the imp. question turning statements.Good Luck!!