ratio

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rahul.s: Master | Next Rank: 500 Posts; Posts: 324; Joined: Thu Dec 24, 2009 6:29 amFollowed by: 1 member; Thanked: 17 times

by rahul.s » Mon Feb 08, 2010 1:48 am

3 machines have a productivity ratio of 1:2:5. all 3 machines are working on a job for 3 hours. at the beginning of the 4th hour, the slowest machine breaks. it is fixed at the beginning at hour 7, and begins working again. the job is done in 9 hours. what was the ratio of the work performed by the fastest machine to the work performed by the slowest?

again, there are no answer options

OA: [spoiler]15:2[/spoiler]

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Source: Beat The GMAT — Problem Solving | Mon Feb 08, 2010 1:48 am

shashank.ism: Legendary Member; Posts: 1022; Joined: Mon Jul 20, 2009 11:49 pmFollowed by: 2 members; Location: Gandhinagar; Thanked: 41 times

by shashank.ism » Mon Feb 08, 2010 2:08 am

rahul.s wrote:3 machines have a productivity ratio of 1:2:5. all 3 machines are working on a job for 3 hours. at the beginning of the 4th hour, the slowest machine breaks. it is fixed at the beginning at hour 7, and begins working again. the job is done in 9 hours. what was the ratio of the work performed by the fastest machine to the work performed by the slowest?

again, there are no answer options

OA: [spoiler]15:2[/spoiler]

3 machines have a productivity ratio of 1:2:5.
Let x be the production of slowest machine per hour. so productivion per hour of middle machine 2x and production of fastest machine 5x
so total production per hour = x+2x+5x =8x.

production by slowest machine in 3 hr + work done in the last 3 hrs = 6x
production by middle machine in 9 hr = 2x9 = 18x
production by fastest machine in 9 hr = 5x9 = 45x

so ration of work done by fastest machin to slowest = 45/6 = [spoiler]15/2 Ans[/spoiler]

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gauravgundal: Master | Next Rank: 500 Posts; Posts: 199; Joined: Mon Apr 06, 2009 4:15 am; Location: India; Thanked: 13 times

by gauravgundal » Mon Feb 08, 2010 5:24 am

See atlast you need to find
the ratio of work performed by fastest mach. to slowest mach. = Ratio of Productivity of Fastest to slowest mach.
= (5*9x)/(1*6x) [9 hrs work by fastest mach.and 6 hrs work by slowest mach. ]
= 15/2

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