Question

.A tap can fill a cistern in 40 minutes and a second tap can
empty the filled cistern in 60 minutes. By mistake
without closing the second tap, the first tap was opened.
In how many minutes will the empty cistern be filled ?​

Answer 1

Answer:

120 min

Step-by-step explanation:

We will assume the time required to be x.

Then we will subtract the work done by tap B from work done by tap A.

(Rate of filling by A-Rate of filling by B)×time=1

here 1 on RHS denotes the full cistern.