Question 6 (nov. 15th)

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bacali: Master | Next Rank: 500 Posts; Posts: 245; Joined: Thu Aug 16, 2007 12:41 pm

by bacali » Sat Nov 15, 2008 4:59 pm

Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete te job in 8 days?

A) 2
B) 3
C) 4
D) 6
E) 8

OA: B

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Source: Beat The GMAT — Problem Solving | Sat Nov 15, 2008 4:59 pm

dmateer25: Community Manager; Posts: 1049; Joined: Sun Apr 06, 2008 5:15 pmFollowed by: 27 members; Location: Pittsburgh, PA; Thanked: 113 times; GMAT Score:710

by dmateer25 » Sat Nov 15, 2008 5:49 pm

https://www.beatthegmat.com/work-problem-t15889.html

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Sat Nov 15, 2008 5:51 pm

6 machines takes 12 days to finish a job
1 machine will take 72 days

To finsih a job in 72 days 1 machine is needed
To finish a job in 8 days of of machines needed will be 72/8 = 9 machines

Differecne = 9-6 =3

3 additional machines needed

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canuckclint: Master | Next Rank: 500 Posts; Posts: 154; Joined: Tue Aug 26, 2008 12:59 pm; Location: Canada; Thanked: 4 times

by canuckclint » Sat Nov 15, 2008 6:56 pm

From the general formula:
6(1/x) = 1/12
Then for n more machines:
6/x + n/x = 1/8

Substitute:
1/12 + n/(12*6) = 1/8

n = 3

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