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Question

A tank of capacity 60 litres can be filled in 10 minutes by a pipe P. Another pipe Q placed at the bottom of tank can empty the tank in 30 minutes. Both of the pipes were opened. In how much time pipe Q will empty the tank if pipe P is closed after 10 minutes?

CAT 2021

A
11 minutes
CORRECT ANSWER WRONG ANSWER
B
12 minutes
CORRECT ANSWER WRONG ANSWER
C
13 minutes
CORRECT ANSWER WRONG ANSWER
D
9 minutes
CORRECT ANSWER WRONG ANSWER
Solution

Correct option is (C)

(C)

Explanatory Answer :

part of tank filled in 1 minute by pipe P = 60/10 = 6 litres

part of tank emptied in 1 minute by pipe Q = 60/30 = 2 litres

part of tank filled by pipe P and Q together in 1 minute= 6 - 2 = 4 litres

part of tank filled by pipe P and Q together in 10 minutes =10*4 = 40 litres

time taken by Q to empty 40 litres = 40/2 = 20 minutes

20 is the correct answer