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Re: Working alone at their respective constant rates, Audrey can complete [#permalink]
"Extra time taken = total break time taken by Ferris = (2*60 - 12*60/7) minutes = 120/7 minutes."

I don't understand what you have done here.

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Re: Working alone at their respective constant rates, Audrey can complete [#permalink]
amorphous wrote:
"Extra time taken = total break time taken by Ferris = (2*60 - 12*60/7) minutes = 120/7 minutes."

I don't understand what you have done here.

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Since they could complete a work in 12/7 hour if worked together but they actually completed it in 2 hours. So extra time taken ((2*60 - 12*60/7) mins) should be equal to total break time for ferris.
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Re: Working alone at their respective constant rates, Audrey can complete [#permalink]
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saurabhhjjain wrote:
Q : Working alone at their respective constant rates, Audrey can complete a certain job in 4 hours, while Ferris can do the same job in 3 hours. Audrey and Ferris worked together on the job and completed it in 2 hours, but while Audrey worked this entire time, Ferris worked for some of the time and took 3 breaks of equal length. How many minutes long was each of Ferris's break?

(A) 5
(B) 10
(C) 15
(D) 20
(E) 25


Audrey can complete a certain job in 4 hours, while Ferris can do the same job in 3 hours.
So, Audrey's RATE = 1/4 of the job per hour
And Ferris' RATE = 1/3 of the job per hour

Audrey and Ferris worked together on the job and completed it in 2 hours, but while Audrey worked this entire time, Ferris worked for some of the time and took 3 breaks of equal length.
Since Audrey works for the entire 2 hours, let's determine how much work she does.
At a rate of 1/4 of the job per hour, Audrey can complete 1/2 of the job in TWO hours.

This means Ferris must have completed the other 1/2 of the job

Time = output/rate
So, Ferris' work time = (1/2)/(1/3) = 3/2 hours = 90 MINUTES

So, at his normal rate of work, Ferris can complete his half of the job in 90 MINUTES, which meanshe rested for the other 30 minutes.


How many minutes long was each of Ferris's break?
Ferris took 3 breaks of equal length
If he rested for a TOTAL of 30 minutes, each break was 10 minutes long.

Answer: B

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Brent
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Re: Working alone at their respective constant rates, Audrey can complete [#permalink]
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saurabhhjjain wrote:
Thanks Amorphous. Can you please tell why my approach is incorrect?

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Your approach doesn't work, because it assumes that BOTH people worked together to complete the job in 120/7 minutes, and then they BOTH rested for the remaining 20/7 minutes.
In actuality, Ferris is the only person who rested.

Cheers,
Brent
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Re: Working alone at their respective constant rates, Audrey can complete [#permalink]
Thank you Brent.
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Re: Working alone at their respective constant rates, Audrey can complete [#permalink]
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I've attached how I did it.
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daum_equation_1565874520871.png
daum_equation_1565874520871.png [ 297.68 KiB | Viewed 11011 times ]

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Re: Working alone at their respective constant rates, Audrey can complete [#permalink]
tricky question. thanks for the solution!
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Re: Working alone at their respective constant rates, Audrey can complete [#permalink]
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