Lights at Hotel California

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sam2304: Legendary Member; Posts: 1239; Joined: Tue Apr 26, 2011 6:25 amFollowed by: 26 members; Thanked: 233 times; GMAT Score:680

by sam2304 » Sat Jan 07, 2012 6:05 pm

Eighty percent of the lights at Hotel California are on at 8 p.m. a certain evening. However, forty percent of
the lights that are supposed to be off are actually on and ten percent of the lights that are supposed to be on
are actually off. What percent of the lights that are on are supposed to be off?
A.22(2/9)%
B.16(2/3)%
C.11(1/9)%
D.10%
E.5%

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Source: Beat The GMAT — Problem Solving | Sat Jan 07, 2012 6:05 pm

chieftang: Master | Next Rank: 500 Posts; Posts: 218; Joined: Wed Nov 23, 2011 8:05 pmFollowed by: 4 members; Thanked: 26 times

by chieftang » Sat Jan 07, 2012 6:45 pm

FYI: https://www.beatthegmat.com/percentages-t98432.html

Chieftang's Combinatorics Notes
Mediant Fractions
Harmonic Mean

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Sun Jan 08, 2012 4:17 am

For the weighted average approach, check the link offered by chieftang:

https://www.beatthegmat.com/percentages-t98432.html

An alternate approach is to plug in the answer choices. Check here:

https://www.beatthegmat.com/mgmat-t82447.html

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ronnie1985: Legendary Member; Posts: 626; Joined: Fri Dec 23, 2011 2:50 amFollowed by: 10 members; Location: Ahmedabad; Thanked: 31 times

by ronnie1985 » Mon Jan 09, 2012 3:21 am

QED
(D) 10% is answer.

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