A pipe can fill a tank in 10 minutes while another pipe can empty it in 12 minutes. If the pipes are opened alternately each for 1 minute, beginning with the first pipe. the tank will be full after (in minutes):
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 109
Let the capacity of tank be LCM of 10 & 12 i.e 60 units
Efficiency = Total work/Total time taken
Efficiency of 1st pipe = 60/10 = 6
Efficiency of 2nd pipe = 60/12 = -5
If the pipes are opened alternately each for 1 minute, beginning with the first pipe
It means work done in 2 minutes = 6 - 5 = 1 Hence 54 units work done in 54 × 2 = 108 minutes then in next minute 6 unit work will done by pipe 1st Hence total time taken is 108 + 1 = 109 minutes