Question

2. A cistern can be filled up by two pumps
in 20 minutes and 30 minutes respec.
tively. They are made to run jointly.
but for technical fault the 2nd pump
was run alone lastly for 10 minutes.
For what time they are run jointly?
(a) 4 minutes (b) 6 minutes
(c) 8 minutes (d) 10 minutes​

Answer 1

Question ⤵️

A cistern can be filled up by two pumps in 20 minutes and 30 minutes respectively. They are made to run jointly but for technical fault the 2nd pump was run alone lastly for 10 minutes. For what time they are run jointly?

Answer ⤵️

Option C is the correct answer.

Reason ⤵️

According to questions, Pipe 'A' is closed after some time. and Tank is filled in 18 miuntes so B started filling the tank in beginning and worked till last i.e 18 minutes

So,2×182×18= 36 units is filled

Work left = 60−36=2460−36=24 units

This 24 units must be filled by ,Pipe A in beginning.

It can flll it in 243243 = 8 minutes