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# Lois can complete a certain job in x hours and Parnel can complete the

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Math Expert
Joined: 02 Sep 2009
Posts: 51184
Lois can complete a certain job in x hours and Parnel can complete the  [#permalink]

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04 Apr 2017, 04:28
00:00

Difficulty:

5% (low)

Question Stats:

98% (00:40) correct 3% (01:59) wrong based on 60 sessions

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Lois can complete a certain job in x hours and Parnel can complete the same job in y hours. Which of the following expresses, in terms of x and y, the time it would take them to complete the job if they worked together?

A. (x + y)/y
B. xy/y
C. xy/x
D. 2/(xy)
E. xy/(x + y)

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Manager
Status: active
Joined: 25 Jan 2016
Posts: 134
Location: India
Concentration: Finance, Entrepreneurship
GPA: 4
WE: Web Development (Computer Software)
Re: Lois can complete a certain job in x hours and Parnel can complete the  [#permalink]

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04 Apr 2017, 04:47

1/x + 1/y=Combined rate
time taken would be xy/(x+y)
Manager
Joined: 14 Sep 2016
Posts: 60
Concentration: Finance, Economics
Lois can complete a certain job in x hours and Parnel can complete the  [#permalink]

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04 Apr 2017, 05:42
Bunuel wrote:
Lois can complete a certain job in x hours and Parnel can complete the same job in y hours. Which of the following expresses, in terms of x and y, the time it would take them to complete the job if they worked together?

A. (x + y)/y
B. xy/y
C. xy/x
D. 2/(xy)
E. xy/(x + y)

E.
Pick numbers

Lois
Job in 10 hours
X=10
$$\frac{1}{10}$$ job an hour

Parnel
Job in 5 hours
Y =5
$$\frac{1}{5}$$ job an hour

Together
x + y = $$\frac{3}{10}$$ job an hour
or 3.33 hours to do the job together.

Plug in x=10 and y=5 into the answer choices until you find 3.33 which is E.
Manager
Joined: 09 Oct 2016
Posts: 89
Location: United States
GMAT 1: 740 Q49 V42
GPA: 3.49
Re: Lois can complete a certain job in x hours and Parnel can complete the  [#permalink]

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04 Apr 2017, 06:02
1/x + 1/y (t) = 1

(x+y)/xy * (t) = 1

t = xy/(x+y)

E

Sent from my iPhone using GMAT Club Forum
Manager
Joined: 06 Dec 2016
Posts: 249
Re: Lois can complete a certain job in x hours and Parnel can complete the  [#permalink]

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04 Apr 2017, 11:55
1/x + 1/y
y +x/xy
Flip over the fraction

xy/y + x

Intern
Joined: 29 Oct 2017
Posts: 5
Location: Russian Federation
GPA: 3.43
WE: Supply Chain Management (Manufacturing)
Re: Lois can complete a certain job in x hours and Parnel can complete the  [#permalink]

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18 Aug 2018, 05:36
WORK = TIME x RATE
WORK = 1
T(L)=X, R(L)=1/X
T(P)=Y, R(P)=1/Y

Rate Together= 1/x+1/y= (y+x)/xy
Time together= Work/Rate=1/((y+x)/xy)= xy/(y+x)
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Re: Lois can complete a certain job in x hours and Parnel can complete the  [#permalink]

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18 Aug 2018, 06:29
Bunuel wrote:
Lois can complete a certain job in x hours and Parnel can complete the same job in y hours. Which of the following expresses, in terms of x and y, the time it would take them to complete the job if they worked together?

A. (x + y)/y
B. xy/y
C. xy/x
D. 2/(xy)
E. xy/(x + y)

Let th total work be xy units

The efficiency of Lois is $$y$$ units/hr
The efficiency of Parnel is $$x$$ units/hr

Combined efficiency of Lois & Parnel is $$(x + y)$$ units/hr

So, the time required by Lois & Parnel is $$\frac{xy}{(x + y)}$$

PS : THIS IS BASICALLY A FORMULA, KNOWING THIS FORMULA CAN HELP DURING THE EXAM
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Abhishek....

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Manager
Joined: 20 Jul 2018
Posts: 89
GPA: 2.87
Re: Lois can complete a certain job in x hours and Parnel can complete the  [#permalink]

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18 Aug 2018, 08:08
rate of Lois = 1/x
rate of Parnel = 1/y
combined rate = 1/x + 1/y = x+y/xy

so time = 1/rate = xy/x+y

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Hasnain Afzal

"When you wanna succeed as bad as you wanna breathe, then you will be successful." -Eric Thomas

Re: Lois can complete a certain job in x hours and Parnel can complete the &nbs [#permalink] 18 Aug 2018, 08:08
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