A tank can be filled by a tap in 20 minutes and by another tap in 60 minutes Both the taps are kept ...........

Quant (SSC) Pipes&cistern

A tank can be filled by a tap in 20 minutes and by another tap in 60 minutes. Both the taps are kept open for 10 minutes and then the first tap is shut off. After this, the tank will be completely filled in what time ?

10 mins

15 mins

20 mins

25 mins

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Explanation:

First we will calculate the work done for 10 mins, then we will get the remaining work, then we will find answer with one tap work, As
Part filled by Tap A in 1 min = 1/20
Part filled by Tap B in 1 min = 1/60
(A+B)'s 10 mins work =
10∗(1/20+1/60)=10∗4/60=2/3
Remaining work = 1−2/3=1/3
METHOD 1
=>1/60:1/3=1:X
=>X=20
METHOD 2
1/60 part filled by B in=1min
1/3 part will be filled in=1/3/1/60=60/3=20