Given that one hose can fill a pool in 90 min and another can fill the pool in 60 minutes, to get how long the 2 hoses will take to fill the pool given that they are running together, we shall simply get the GCF of the times takes by the hoses, thus we shall have:
Multiples of 60 are
2,2,3,5
Multiples of 90
2,3,3,5
thus the GCF is: 2×3×5=30
Thus the two hoses working together will take 30 min
