Question

Two pipes A and B can seperately fill a tank in 20 minutes and 30 minutes respectively while a third pipe C can empty it in 15 minutes if all the three pipes are used simultaneously in how much time will the tank be filled

Answer 1

Step-by-step explanation:

A can fill 1/20 part of the tank in 1 minute

B can fill 1/30 part of the tank in 1 minute

C can empty 1/15 part of the tank in 1 minute

thus the tank will fill in 1/20 +1/30 + 1/15 =

3/20 part of the tank will fill in minute

6 minute 40 seconds

Answer 2

A can fill it in 20 minutes

in 1 minute, A can fill = 1/20 of the tank

B can fill it in 30 minutes

in 1 minute, B can fill = 1/30 of the tank

C can empty it in 15 minutes

in 1 minute, C can empty = 1/15 of the tank

If all taps are opened at once, In 1 minute portion of tank filled

= portion filled by A and B - portion emptied by C

$= \frac{1}{20} + \frac{1}{30} - \frac{1}{15} \\ \\ = \frac{1 \times 3 + 1 \times 2 - 1 \times 4}{60}\\ \\ = \frac{3+2-4}{60} \\ \\ = \frac{1}{60}$

So in 1 minute, 1/60 of the tank is filled

time need to fill it completely = 60/1 = 60 minute.

Tank will be filled in 60 minutes