Latest Elitmus Aptitude Question SOLUTION: A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will t

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(#M40164239) ELITMUS Numerical Ability question Keep an EYE

A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will the cistern be filled?

Asked In Elitmus Sniper (7 years ago)

Unsolved Read Solution (4)

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rajat bhawsar  (7 years ago)

ans is 2 hours

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rajesh dharamdasani  (7 years ago)

TAP -A -20 mints -> 3 L/mint
TAP -B - 30 mints -->2 L/mint
Tank will be full in 60 mints

so A-B+A-B+A-B..................... = TF
=> 1.5-1 = 0.5
1 * 60 = 60 mints
0.5 * 120 mints or 2 hrs

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kundan  (6 years ago)

Total unit of work = 60(lcm of 20 and 30)
a's efficiency=3, b's efficiency= -2
therefore net amount of work done in 2 min = 1 unit
now in 57 min, i.e actually 114 min, work done is 57/60
remaining 1/20 work will be done by a in 1 min, i.e 115 min is the answer
It can also be done by fraction:
1/20 - 1/30 = 1/60
and proceeding as above

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swati  (6 years ago)

A 1 min work=1/20
B 1 min work= -1/30
A/q
=>A+B+A+B+....=1(total work)
1/20-1/30+1/20-1/30....=1
1/60+1/60+1/60+....=1
means 1/60 work is done in 2 min
1 work is done in=2*60=120min or 2hr (ans)

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