Two pipes can fill a tank in 15 min and 20 min respectively. Due to some blockage in pipes, only \(\frac{1}{2}\) water and \(\frac{2}{3}\) water can flow through first and second pipe respectively. After removing that blockage, the tank filled in 5 minutes. After how much time the blockage was removed?
Answer & explanation
Correct answer: option 2
A(+) : B(-)
15 : 20 Time
4 : 3 Efficiency
Total work = 60 (LCM of 15 and 20)
In last five minutes, the work done will be 5 x 7 = 35
Remaining work = 60 - 35 = 25
Due to blockage, efficiency of pipe A is \(\frac{4}{2}\) = 2 and that of pipe B is \(\frac{6}{3}\) = 2
Time taken to fill 25 ltrs. = \(\frac{work}{efficiency}\) = \(\frac{25}{4}\) = 6 \(\frac{1}{4}\) = 6 min 15 seconds
Hence,
The blockage was removed after 6 min 15 sec.