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# Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs a

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Joined: 02 Sep 2009
Posts: 60646
Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs a  [#permalink]

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07 Jan 2020, 06:08
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Difficulty:

45% (medium)

Question Stats:

67% (02:40) correct 33% (02:47) wrong based on 30 sessions

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Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs and 25 hrs respectively. At first all the taps are opened simultaneously. After 2 hours tap C is closed and after further 2 hours tap B is also closed. Tap A is kept open till the tank gets completely filled. What fraction of the tank is filled by tap A?

A. 2/11
B. 9/11
C. 18/25
D. 7/25
E. 1/2

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Re: Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs a  [#permalink]

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13 Jan 2020, 09:17
work of C = 2/25
work of B = 4/20 ; 1/5
total work done ; 7/25
left with 18/25
A has to do 18/25
IMO C

Bunuel wrote:
Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs and 25 hrs respectively. At first all the taps are opened simultaneously. After 2 hours tap C is closed and after further 2 hours tap B is also closed. Tap A is kept open till the tank gets completely filled. What fraction of the tank is filled by tap A?

A. 2/11
B. 9/11
C. 18/25
D. 7/25
E. 1/2
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Re: Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs a  [#permalink]

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14 Jan 2020, 07:55
1
Bunuel wrote:
Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs and 25 hrs respectively. At first all the taps are opened simultaneously. After 2 hours tap C is closed and after further 2 hours tap B is also closed. Tap A is kept open till the tank gets completely filled. What fraction of the tank is filled by tap A?

A. 2/11
B. 9/11
C. 18/25
D. 7/25
E. 1/2

Let the capacity of the Tank be 100 units

Efficiency of Tap A = 10 Units/Hr
Efficiency of Tap B = 5 Units/Hr
Efficiency of Tap C = 4 Units/Hr

Combined efficiency of the 3 taps is 19 Units/Hr

Water filled up in 2 Hours is 38 Units ; We are left with 62 Units

After 2 Hours C is closed and A and B works at efficiency of 15 Units/Hr , so in 2 Hours they fill up 30 Units; We are left with 32 Units

Next B is also closed and we are left with Tap A to fill up 32 units

Thus, Part of work done by Tap A is 2*10 + 2*10+32 = 72 units out of 100 Units

SO, A does 18/25 part of the job, Answer must be C
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Re: Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs a  [#permalink]

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21 Jan 2020, 08:59
1
Bunuel wrote:
Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs and 25 hrs respectively. At first all the taps are opened simultaneously. After 2 hours tap C is closed and after further 2 hours tap B is also closed. Tap A is kept open till the tank gets completely filled. What fraction of the tank is filled by tap A?

A. 2/11
B. 9/11
C. 18/25
D. 7/25
E. 1/2

Since tap C operates for 2 hours and its rate is 1/25, tap C has filled 2 x 1/25 = 2/25 of the tank.

Similarly, since tap B operates for 4 hours and its rate is 1/20, tap B has filled 4 x 1/20 = 4/20 = 1/5 of the tank.

Therefore, together taps B and C have filled 1/5 + 2/25 = 5/25 + 2/25 = 7/25 of the tank.

Since the rest of the tank is filled by tap A, tap A has filled 1 - 7/25 = 18/25 of the tank.

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Re: Three taps A, B and C can fill a tank individually in 10 hrs, 20 hrs a   [#permalink] 21 Jan 2020, 08:59
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