1 Answers
Option 3 : 690/29
Given:
Pipe A, B are filling pipes that can fill the tank in 45 and 54 minutes.
C can empty the tank in 72 Minutes.
A, C are kept open for 30 minutes, then pipe B and C are opened for 24 minutes.
Calculation:
Let us take the LCM of the time of the three pipes i.e.
LCM of (45, 54, 72) minutes = 1080 units. ----(1)
Let 1080 units be the capacity of the tank.
⇒ Efficiency of A = (1080/45) = 24 units
⇒ Efficiency of B = (1080/54) = 20 units
⇒ Efficiency of C = (1080/72) = -15 units
(∵ A, B are filling pipes so their efficiency is positive and as C is an empty pipe, its efficiency is negative)
Work was done By A, C in 30 minutes = (24 - 15) × 30 = 270 unit ----(2)
Now, B, C was opened for 24 minutes,
So, work done by B, C in 24 minutes = (20 - 15) × 24 = 120 units ----(3)
From (1), (2), (3) we get the left work = 1080 - 270 - 120 = 690 unit
Time taken by all three pipes to fill the Remaining tank (690)/(24 + 20 – 15) = 690/29 min.
∴ The time taken by all pipes to fill the remaining tank is 690/29 min.