Question

A large drain and a small drain are opened to drain a pool. The large drain can empty the pool in 6 hours. After both drains have been open for 1 hour, the large drain becomes clogged and is closed. The smaller drain remains open and requires 9 hours more to empty the pool. How long would it have taken the small drain, working alone, to empty the pool?

Answer 1

It would have taken the small drain 11 hours