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A and B can do a piece of work in 72 days; B and C can do it in 120 da

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Bunuel
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A and B can do a piece of work in 72 days; B and C can do it in 120 da [#permalink] New post   08 Feb 2021, 03:30
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A and B can do a piece of work in 72 days; B and C can do it in 120 days; A and C can do it in 90 days. In what time can A alone do it ?

(A) 150 days
(B) 120 days
(C) 100 days
(D) 80 days
(E) 70 days
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B
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meanup
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Re: A and B can do a piece of work in 72 days; B and C can do it in 120 da [#permalink] New post   08 Feb 2021, 21:45
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Ans B

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Geet03
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Re: A and B can do a piece of work in 72 days; B and C can do it in 120 da [#permalink] New post   13 Feb 2021, 00:10
meanup wrote:
Ans B

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Can you please explain how are we calculating efficiency?
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Re: A and B can do a piece of work in 72 days; B and C can do it in 120 da [#permalink] New post   13 Feb 2021, 02:17
1/A + 1/B = 1/72 ----- (i)
1/B + 1/C = 1/120 ---- (ii)
Subtracting (i) and (ii)
1/A - 1/C = 1/180 ---- (iii)
1/A + 1/C = 1/90 ---- (iv)
Adding (iii) and (iv)
2/A = (1+2)/180 = 3/180 = 1/60
2/A = 1/60
1/A = 120
A = 120
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meanup
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A and B can do a piece of work in 72 days; B and C can do it in 120 da [#permalink] New post   13 Feb 2021, 04:37
Geet03 wrote:
meanup wrote:
Ans B

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Can you please explain how are we calculating efficiency?


The efficiency of an individual? It is mentioned to the right in the pic. Firstly, we are calculating the combined efficiency, then we are substituting the eff. of an individual.

Geet03

Let me share another pic with complete detail and please tag me for any further clarification

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Re: A and B can do a piece of work in 72 days; B and C can do it in 120 da [#permalink] New post   10 Feb 2024, 22:34
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Re: A and B can do a piece of work in 72 days; B and C can do it in 120 da [#permalink]
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