Pipe A can fill a tank in 20 hours, pipe B in…

Pipe A can fill a tank in 20 hours, pipe B in 20 hours and pipe C in 30 hours. If all the pipes are open, in how many hours will the tank be filled?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #15582