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A can do a work in 15 days and B can do the same work in 20 days. If..

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Joined: 07 Jul 2012
Posts: 370
Location: India
Concentration: Finance, Accounting
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A can do a work in 15 days and B can do the same work in 20 days. If..  [#permalink]

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11 Oct 2017, 19:11
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Difficulty:

25% (medium)

Question Stats:

68% (00:48) correct 32% (00:58) wrong based on 88 sessions

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A can do a work in 15 days and B can do the same work in 20 days. If they work together for 4 days, then the fraction of work that has left is:

A) $$\frac{1}{4}$$

B) $$\frac{1}{5}$$

C)$$\frac{1}{10}$$

D) $$\frac{7}{15}$$

E) $$\frac{8}{15}$$

Kindly hit kudos if my post helps!

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Kindly hit kudos if my post helps!

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Joined: 07 Sep 2017
Posts: 8
Location: Australia
Re: A can do a work in 15 days and B can do the same work in 20 days. If..  [#permalink]

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11 Oct 2017, 19:37
1- [1/15+1/20]*4
= 1-7/15
=8/15
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Joined: 22 May 2016
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A can do a work in 15 days and B can do the same work in 20 days. If..  [#permalink]

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12 Oct 2017, 08:26
3
varun4s wrote:
A can do a work in 15 days and B can do the same work in 20 days. If they work together for 4 days, then the fraction of work that has left is:

A) $$\frac{1}{4}$$

B) $$\frac{1}{5}$$

C)$$\frac{1}{10}$$

D) $$\frac{7}{15}$$

E) $$\frac{8}{15}$$

Kindly hit kudos if my post helps!

This question has a wrinkle: it asks for work remaining, not work finished.

A's rate, W/day = $$\frac{1}{15}$$

B's rate, W/day = $$\frac{1}{20}$$

Add rates with LCM of 60. Together, their rate is $$\frac{4}{60} + \frac{3}{60}$$ =$$\frac{7}{60}$$

They work together at this rate for t = 4 days. $$rt=W$$

They finish: $$(\frac{7}{60} * 4) =\frac{28}{60} =\frac{7}{15}$$

Fraction of work that is left

($$1 -\frac{7}{15}) =(\frac{15}{15} - \frac{7}{15}) =\frac{8}{15}$$

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Re: A can do a work in 15 days and B can do the same work in 20 days. If..  [#permalink]

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16 Oct 2017, 16:57
varun4s wrote:
A can do a work in 15 days and B can do the same work in 20 days. If they work together for 4 days, then the fraction of work that has left is:

A) $$\frac{1}{4}$$

B) $$\frac{1}{5}$$

C)$$\frac{1}{10}$$

D) $$\frac{7}{15}$$

E) $$\frac{8}{15}$$

We use the formula work = rate x time. The work completed in 4 days is:

(1/15) x 4 + (1/20) x 4 = 4/15 + 4/20 = 16/60 + 12/60 = 28/60 = 7/15

In 4 days, we see that 7/15 of the job has been completed. So, 1 - 7/15 = 15/15 - 7/15 = 8/15 of the job is left to be completed.

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A can do a work in 15 days and B can do the same work in 20 days. If..  [#permalink]

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16 Oct 2017, 20:59
2
In 1 day, A finishes 1/15 job
In 1 day, B finishes 1/20 job
Totally, in 1 day, both A and B finish (1/15 +1/20) = 7/60 job

In 4 days, both A and B finish 4x7/60 = 7/15 job.
After 4 days, the remaining job is 1-7/15 = 8/15 job.

Please kudo if it helps. Thanks.
A can do a work in 15 days and B can do the same work in 20 days. If.. &nbs [#permalink] 16 Oct 2017, 20:59
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