Hey Swabs!  We are late.  Like late, late.  Like too late for plan B late.  It's not that, at least I hope not, we are mostly late because we have been trying to work this out: 

Two large and 1 small pumps can fill a swimming pool in 4 hours. One large and 3 small pumps can also fill the same swimming pool in 4 hours. How many hours will it take 4 large and 4 small pumps to fill the swimming pool.(We assume that all large pumps are similar and all small pumps are also similar.)

Please let us know if you find it...