A large fresh water reservoir has two types of drainage system: small pipes and large pipes.
[Ref: ZHRT] © Kevin Stone
6 large pipes, on their own, can drain the reservoir in 12 hours.
3 large pipes and 9 small pipes, at the same time, can drain the reservoir in 8 hours.
How long will 5 small pipes, on their own, take to drain the reservoir?
Hint: The exact size of the pipes and reservoir does not matter.
Back to the puzzles...