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

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