1 Answers
Option 3 : 30 minutes
Let the inlet taps be A and B, and outlet taps be C and D.
As, Tap A can fill the tank in 10 minutes
⇒ Part of tank filled by A in 1 minute = 1/10
Also, Tap B can fill the tank in 15 minutes
⇒ Part of tank filled by tap B in 1 minute = 1/15
⇒ Part of tank filled by Tap A and B in 1 minute = (1/10) + (1/15) = 1/6
Now, Tap C can empty the tank in 12 minutes
⇒ Part of tank emptied by tap C in 1 minute = 1/12
Also, Tap D can empty the tank in 20 minutes
⇒ Part of tank emptied by tap D in 1 minute = 1/20
⇒ Part of tank emptied by tap C and D in 1 minute = (1/12) + (1/20) = 2/15
⇒ Effective filling of tank in 1 minute when all the taps are open = (1/6) – (2/15) = 1/30
∴ The tank will be filled in 30 minutes