1 Answers
Option 3 : 100 minutes
Given:
Pipe P + Pipe Q = 60/7 minutes
Pipe P + Pipe Q - Pipe R = 300/23 minutes
Pipe P : Pipe Q = 3 : 4
Formula:
If time taken by pipe A to fill tank is ‘a’ minutes and by pipe B is ‘b’ minutes then total time taken to fill the tank t ⇒ (1/t) = (1/a) + (1/b)
Calculation:
Let, time taken by pipe P be X
⇒ Time taken by pipe Q = 4 × X/ 3
⇒ 7/ 60 = (1/ X) + (3/(4X))
⇒ 7/ 60 = (4 + 3)/4X
⇒ 7/ 60 = 7/4X
⇒ 60 = 4X
⇒ X = 15
⇒ Time taken by pipe Q = 20 (∵ 4 × 15/3 = 20)
Let, time taken by pipe R be Y
⇒ 23/ 300 = (7/ 60) - (1/Y)
⇒ 1/ Y = (7/ 60) + (23/300)
⇒ 1/ Y = (35 – 23)/300
⇒ Y = 25 (∵ 300/12 = 25)
Now finding time taken by Q and R to fill the tank
⇒ 1/ t = (1/ 20) - (1/25)
⇒ 1/ t = (25 - 20)/500
⇒ 1/ t = 1/100
⇒ t = 100/1 minutes
∴ it takes 100 minutes to fill the tank
Confusion PointsTime taken by two pipe to fill a tank is 60/ 7 = 8.57 min (approx.)
Time taken by three pipe to fill a tank is 300/ 23 = 13 min (approx.)
As three pipe together takes more time than two pipes.
That means the one pipe drain pipe taking water out of tank.
Hence, R time is been subtracted.