work problem2

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prameko: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Fri Apr 11, 2008 7:58 am

work problem2

by prameko » Tue Apr 15, 2008 12:57 pm

Please explain me in the fast way to solve this problem. I always have problem with work problem. What is the concept to solve this kind of problem?

Lindsay can paint 1/x of a certain room in 20 minutes. What fraction of the same room can Joseph paint in 20 minutes if the two of them can paint the room in an hour, working together at their respective rates?

a. 1/3x

b. 3x/x – 3

c. x – 3/3x

d. x/x – 3

e. x – 3/x

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Source: Beat The GMAT — Problem Solving | Tue Apr 15, 2008 12:57 pm

prabhu3645: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Thu Apr 03, 2008 11:49 am

Is the anwere B

by prabhu3645 » Tue Apr 15, 2008 2:58 pm

L=20x
1/L + 1/J = 1/60
therefore 1/J = 1/60 - 1/20x or J = 60x/(x-3) and threfore in 20 minutes it should be 3x/x-3.

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netigen: Legendary Member; Posts: 631; Joined: Mon Feb 18, 2008 11:57 pm; Thanked: 29 times; Followed by:3 members

Are the answers correct

by netigen » Tue Apr 15, 2008 3:44 pm

Simplest way to solve is this:

L does 1/x work in 20 min so she will do 3/x in 60 min

3/x + J's work in 60 = 1

J's work in 60 min = 1-(3/x)

J's work in 20 mins = (1/3) * (1-[3/x]) = (x-3)/3x