Question

There are three pipes in which a cistern can be filled. The second takes 5 hours longer than the first, the third three times as long as the first. If all are open the cistern can be filled in 2 and 1/4 hours. How long would it take each alone to fill the cistern?

Answer 1

If the first takes x hours,

1/x + 1/(x+5) + 1/(3x) = 1/(9/4)
x = 4

So, the 3 pipes require 4,9,12 hours.