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# A works twice as fast as B. If B can complete a piece of work independ

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Math Expert
Joined: 02 Sep 2009
Posts: 58340
A works twice as fast as B. If B can complete a piece of work independ  [#permalink]

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30 Jan 2019, 03:02
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Difficulty:

5% (low)

Question Stats:

88% (00:51) correct 13% (01:04) wrong based on 55 sessions

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A works twice as fast as B. If B can complete a piece of work independently in 12 days, then the number of days taken by A and B together to finish the work is:

A. 4
B. 6
C. 8
D. 9
E. 10

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Re: A works twice as fast as B. If B can complete a piece of work independ  [#permalink]

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30 Jan 2019, 03:26
2
Since A is twice as efficient as B; A takes 6 days to finish a job.

Together = 1/6+1/12 = 3/12 = 4 days.

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Re: A works twice as fast as B. If B can complete a piece of work independ  [#permalink]

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30 Jan 2019, 03:35
Bunuel wrote:
A works twice as fast as B. If B can complete a piece of work independently in 12 days, then the number of days taken by A and B together to finish the work is:

A. 4
B. 6
C. 8
D. 9
E. 10

rb=x/12

ra=2 * rb = x/6
together
x/6+x/12 =
x=4
IMO A
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Re: A works twice as fast as B. If B can complete a piece of work independ  [#permalink]

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01 Feb 2019, 19:08
1
Bunuel wrote:
A works twice as fast as B. If B can complete a piece of work independently in 12 days, then the number of days taken by A and B together to finish the work is:

A. 4
B. 6
C. 8
D. 9
E. 10

We can see that the rate of B = 1/12, and hence the rate of A = 2 x 1/12 = 1/6. Thus, their combined rate is:

1/6 + 1/12 = 2/12 + 1/12 = 3/12 = 1/4.

So it will take 4 days to complete the job when working together.

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Re: A works twice as fast as B. If B can complete a piece of work independ  [#permalink]

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01 Feb 2019, 21:05
Bunuel wrote:
A works twice as fast as B. If B can complete a piece of work independently in 12 days, then the number of days taken by A and B together to finish the work is:

A. 4
B. 6
C. 8
D. 9
E. 10

rate of B rB = W/12

rate of A rA = W/6

rB + rA = W/x

W/12 + W/6 = W/x

x = 4

A
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Re: A works twice as fast as B. If B can complete a piece of work independ   [#permalink] 01 Feb 2019, 21:05
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