The water from one outlet, flowing at a constant rate, can fill a swimming pool in 9 hours. The water from a second outlet, flowing at a constant rate, can fill the same pool in 5 hours. If both outlets are used at the same time, approximately what is the number of hours required to fill the pool?
(A) 0.22 (B) 0.31 (C) 2.50 (D) 3.21 (E) 4.56
Always remember RT=W i.e Rate*Time = Work
Also remember that rate can be added or subtracted. For e.g if A do a work in 2 day and B do a work in 2 day.
They both of them together will do a work in 1 day.
So now your question first determine both outlets rate.
1st outlet rate = 1/9 (R=W/T here W=1 work, T = 9hrs)
2nd outlet rate = 1/5 (R=W/T here W=1 work, T = 5hrs)
Both of them working together rate = 1st outlet rate + 2nd outlet rate = 1/9+1/5 = 14/45
again apply the formula RT=W
T = W/R = 1/14/45 = 45/14 =3.21
Answer is D.
Hope this helps.
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