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Question

A cistern of capacity 40 litres has an inlet and an outlet pipe. When both the pipes are opened at once, it takes 8 minutes to fill the cistern. However, if the outflow rate is increased 1.5 times, the cistern never gets filled. Which of the following can be the outflow rate?

CAT 2021

A
8 litres/minute
CORRECT ANSWER WRONG ANSWER
B
6 litres/minute
CORRECT ANSWER WRONG ANSWER
C
12 litres/minute
CORRECT ANSWER WRONG ANSWER
D
9 litres/minute
CORRECT ANSWER WRONG ANSWER
Solution

Correct option is

(C)

Explanatory Answer :

Initially, net flow in the tank = 40 litres/ 8 minutes = 5 litres/minute

Now, the increase in outflow should be greater than 5 litres/min for the tank to fill up.

Increase in outflow = 1.5x – x = 0.5x

in option C, we have , 0.5 * 12 = 6 litres/min > 5 litres/min

Hence, the answer is "12 litres/minute".

so , C is the correct option