| A water tank has two pipes. The empty tank is filled in 12 min by the 1st and the full tank is emptied by the 2nd in 20 min. The time required to fill the 1/2 full tank when both pipes are in action, is [SSC (CGL) 2014] |
A) 16 min
B) 15 min
C) 20 min
D) 30 min
Correct Answer: B
Solution :
(b)| Since, 1st pipe takes 12 min to completely fill the tank. |
| \[\therefore \]Tank filled by 1st pipe in 1 min \[=\frac{1}{12}\] |
| Now, 2nd pipe takes 20 min to empty the full tank. |
| \[\therefore \]Tank emptied by 2nd pipe in minute \[=\frac{1}{20}\] |
| Now, time taken by both pipes to fill complete tank |
| \[=\frac{1}{12}-\frac{1}{20}=\frac{5-3}{60}=\frac{2}{60}=\frac{1}{30}\] |
| Since, total tank will be filled in 30 min. |
| Hence, time taken to fill the half tank \[=\frac{30}{2}=15\min \] |
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