Question

Two pipes can fill a tank in 15 min and 20 min respectively. A third pipe at the bottom empties the tank in 30 min. find the time
required to fill a tank, which is already = full?
(a) 12 min
(b) 9 min
(c) 8 min
(d) 7 min (e) None of these​

Answer 1

Step-by-step explanation:

Part of the tank filled when all the three pipes are opened in 1 minute =

15

1

Part of the tank filled when (A + B) are opened in 1 minute =

20

1

+

24

1

=

120

6+5

=

120

11

∴ Part of the tank emptied by C in 1 min =

120

11

−

15

1

=

40

1

∴ Capacity of =

40

1

part of the tank =3 gallons

∴ Capacity of the tank =(3×40) gallons =120 gallons