Mean

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MI3: Senior | Next Rank: 100 Posts; Posts: 83; Joined: Sat Feb 26, 2011 11:22 amFollowed by: 1 member; Thanked: 1 times

by MI3 » Sat Jul 16, 2011 5:01 am

Q. If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the mean M of the set increase?
(1) Z = 60 (2) N = Z / M

IMO - C, am i correct?

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Source: Beat The GMAT — Data Sufficiency | Sat Jul 16, 2011 5:01 am

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Sat Jul 16, 2011 9:42 pm

MI3 wrote:Q. If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the mean M of the set increase?
(1) Z = 60 (2) N = Z / M

The mean of the set, M = (-14 - 12 + 17 + 28 + 41 + Z)/6 = (60 + z)/6
After multiplication the new mean, M' = (60 + Z)*N/6 = NM

Hence, percentage increase = 100*(NM - M)/M = 100*(N - 1)
Thus, the percentage increase depends only upon the value of N.

Only both statements together, we can determine the value of N.

The correct answer is C.

Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
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