A man has a pool

A man has a pool. This full pool can be drained using four different drainage, if he uses A it takes 10 hours to drain pool, if he uses B it takes 50 hour to drain and if he uses C it takes 5 hours to drain the pool. He first runs the water by A for 5 hours, then turning that off, he continues with B for 10 hours. Then turning that off as well he uses C for 1 hours and lastly using D for 1 hour the pool is empty. How long does it take to empty the pool only using the drainage D?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #83332