1 Answers
Option 5 : 3
Given:
Total number of taps = 9
Time taken by each inlet tap to fill the tank = 20 hours
Time taken by each outlet tap to empty the tank = 30 hours
Total time taken to fill the tank = 5 hours
Concept used:
Total work = Time taken × Efficiency
And, Total efficiency = efficiency of inlet taps – efficiency of outlet taps
Calculation:
Let total number of inlet taps be x
Total number of outlet taps be (9 – x)
L.C.M of 20 and 30 = 60 units = Total work
Total time taken to fill the tank = 5 hours
Efficiency of all 9 taps = 60/5 = 12 units
Efficiency of each inlet tap = 60/20 = 3 units
Now, Efficiency of x inlet taps = 3x
Efficiency of each outlet tap = 60/30 = 2 unit
Efficiency of (9-x) outlet taps = (18 - 2x)
So, Total efficiency of 9 taps = efficiency of inlet taps – efficiency of outlet taps
⇒ Total efficiency of 9 taps = 2x – (18 – 2x)
So, 3x – (18 – 2x) = 12
⇒ 5x – 18 = 12
⇒ 5x = 30
⇒ x = 6
⇒ Outlet taps = (9 – 6) = 3
∴ The number of outlet taps is 3