Question

1. Two pumps can fill a water tank in 20 minutes and 15 minutes
individually. An outlet can empty the full tank in 30 minutes. If
the out let is forgotten to be closed and pumps are switched in
how much time do all of them fill the tank?​

Answer 1

Answer:

Correct option is

A

1800 litres

Part of the tank that can be filled by the two filler taps = (

30

1

+

20

1

)=

60

2+3

=

60

5

=

12

1

∴ The two taps can fill the tank in 12 minutes.

⇒ half of the tank will be filled in 6 minutes.

⇒ The time taken by the remaining half of the tank to be filled when the outlet pipe is open =(24−6) min =18 min.

⇒ Part of that half of the tank that can be emptied in 1 hour =

6

1

−

18

1

=

9

1

∴ Time taken to empty half of the cistern =9 minutes

∴ Capacity of the tank =100×9×2=1800 liters.