ARITHMETICMATHSTIME AND WORK

QUESTIONS ON PIPES & CISTERNS (PART-II)

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QUESTIONS ON PIPES & CISTERNS (PART-II)

QUERY 11

Tap A can fill a tank in 10 minutes and tap B can empty it in 12 minutes. If both the taps are opened alternatively in interval of 1 minute, how much time the tank will take to be filled completely.

A) 1 hour 49 minutes
B) 1 hour 35 minutes
C) 2 hours
D) 1 hour 48 minutes

MAHA GUPTA
Both the taps are kept open alternatively for 1 minute each, we’ll find the part of the tank filled in 2 minutes i.e. one interval of time; so it is 110112 = 1/60

It’s obvious that the tap-B which is emptying the tank will not have to be opened in the last interval, otherwise the tank will never fill; so we need to know the work of the tap-A in the last 1 minute.

So, work of tap-A in 1 minute = 1/10
It does mean both the taps work simultaneously to fill = 1 – 110 = 910 of the tank.

Time taken to fill 1/60 of the tank by both the taps working together = 2 minutes
Hence, time taken in all to fill 9/10 of the tank = (2*60) × 910 = 108 minutes

So, total time to fill the full tank = Time taken for 910 of the part + time taken for 110 of the part
= 108 + 1 = 109 minutes = 1 hour 49 minutes (option ‘A’)

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Maha Gupta

Maha Gupta

Founder of www.examscomp.com and guiding aspirants on SSC exam affairs since 2010 when objective pattern of exams was introduced first in SSC. Also the author of the following books:

1. Maha English Grammar (for Competitive Exams)
2. Maha English Practice Sets (for Competitive Exams)