Question

Pipe A can fill in 20 minutes and Pipe B in 30 mins and Pipe C can empty the same in 40 mins.If all of them work together, find the time taken to fill the tank
(a) 17 1/7 mins
(b) 20 mins
(c) 8 mins
(d) none of these

Answer 1

17 1/7 mins
=(1/20)+(1/30)-(1/40)
=7/120
on taking of reverse we get total time
=17 1/7 mins

Answer 2

Answer:

$17\frac{1}{7}$ minutes

Step-by-step explanation:

Pipe A can fill in 20 minutes

Pipe A can do work in 1 minute = $\frac{1}{20}$

Pipe B can fill in 30 mins

Pipe B can do work in 1 minute = $\frac{1}{30}$

Pipe C can empty the same in 40 mins

Pipe C can do work in 1 minute = $\frac{1}{40}$

So, they can do work together in 1 minute =  $\frac{1}{20}+\frac{1}{30}-\frac{1}{40}$

                                                                      =  $\frac{7}{120}$

They can fill  $\frac{7}{120}$ part in minutes = 1

They can fill  full tank in minutes = $\frac{1}{\frac{7}{120}}$

                                                     = $17\frac{1}{7}$

Hence the time taken to fill the tank is  $17\frac{1}{7}$ minutes