RRB NTPC 29 April 2016 Paper

Question : 10 of 100

Marks: +1, -0

Two pipes, A & B, can fill a tank in 12 & 16 minutes respectively. Both pipes are opened together, but 4 minutes before the tank is full, pipe A is closed. In how many minutes will the tank be full?

9 minutes 8 seconds
10 minutes 9 seconds
11 minutes 19 seconds
11 minutes 29 seconds

Validate

Solution:

(1) Pipe A can fill in 1 min =

1/12

partof tank
Pipe B can fill in 1 min =

1/16

part of tank
Let total time taken be x min
According to the question,

\ { x - 4 } /{ 12 } + \ { x }/ { 16 } = 1

\⇒ \ { 4 x - 16 + 3 x }/ { 48 } = 1

\⇒ 7 x = 48 + 16

\⇒ x = \ { 64 }/ { 7 }

minutes or 9 minutes 8 seconds.

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