problem solving?

Question

Clerk F files a certain quantity of cards in 2 1/2 hours. Clerk G can do the work in 3 hours. At these rates, in how many minutes can Clerk F file alone for 2 hours ?

Answer 1

The question isn't clear to me, but I think it's asking: how long can Clerk F go without Clerk G's help if the filing must be completed within 2 hours?

If so, you can find the answer like this: In 2 hours Clerk F will have done 2 / (2 1/2) = 2 / (5/2) = 4/5 of the work. So Clerk G needs to do 1/5 of the work. This will take him 1/5 of 3 hours, that is to say 36 minutes. So he must share the work for 36 minutes, so Clerk F can be alone for up to (2 hours - 36 minutes) = 1 hour 24 minutes.