Question

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

Answer:

option C is the correct answer