RRB Junior Engineer Stage 1 Model Papers 10

Part filled by first pipe in 1 hour =

1

10

Part filled by second pipe in 1 hour =

1

12

Suppose the waste pipe can empty the full tank in x hours.
Then, part emptied by waste pipe in 1 hour =

1

x

All the three pipes can fill the tank in 20 hours
i.e. part filled by all three pipes in hour =

1

20

Now,
⇒

1

10

+

1

12

−

1

x

=

1

20

⇒

1

x

=

1

10

+

1

12

−

1

20

=

8

60

=

2

15

∴x=

15

2

i.e, the waste pipe can empty the full tank in

15

2

hours
Given that the waste pipe can empty 80 gallons per hour.
Therefore, in

15

2

hours, it can empty

15

2

×80=600 gallons.
Hence, volume of the tank = 600 gallons.