Question 592817
The 1st hose fills this much of the pool per minute: 
1 pool/50 mins = 1/50 pool/min
And the 2nd hose fills 1/30 of the pool every min.

Working together, the fill rate is 1/30 + 1/50 = 10/300 + 6/300 = 16/300 pool/min
Therefore it takes 300/16 = 18.75 mins to fill the pool.