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urooj.khan
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Post subject: what is the average (arithmetic mean) height of the n people  Posted: Sat Jun 13, 2009 5:12 pm |
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what is the average (arithmetic mean) height of the n people of a certain group?
(1) the average height of the n/3 tallest people in the group is 6 feet 2 1/2inches ( in decimal this would be =2.5 inches), and the average height of the rest of the people in the group is 5 feet 10 inches
(2) the sum of the heights of the n people is 178 feet 9 inches
correct answer is A.
is this the most efficient and fastest way to arrive at this answer:
(1) assume n = 10, then the average is [(3)(6 feet 2.5 inches) + (7)(5 feet 10 inches)]/10
sufficient
(2) not sufficient
??
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stock.mojo11
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Post subject: Re: what is the average (arithmetic mean) height of the n people Posted: Sun Jun 14, 2009 9:47 am |
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Posts: 43
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You dont have to necessarily assume n=10.
As soon as you see A, you see that it is a classic weighted average. With weighted averages, to find the whole average, you do not need to know the total number of elements
A is saying { (n/3) (6 2.5) + (2n/3) (5 10) } / n
n's in numerator and denominator get canceled, in any weighted avg problem.
HTH
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RonPurewal
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Post subject: Re: what is the average (arithmetic mean) height of the n people Posted: Mon Jun 15, 2009 10:44 pm |
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| ManhattanGMAT Staff |
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RonPurewal
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Post subject: Re: what is the average (arithmetic mean) height of the n people Posted: Mon Jun 15, 2009 10:44 pm |
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| ManhattanGMAT Staff |
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