Machine A working alone can complete a job in 3 hours

Machine A working alone can complete a job in 3 hours. Machine B working alone can do the same job in 4 hours. How long will it take both machines working together at their respective constant rates to complete the job?

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 #5068