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Average height

by Baldini » Thu Apr 02, 2009 7:52 am
What is the average height (arithmetic mean) of the n people in a certain group?

1. The average height of the n/3 tallest people in the group is 6 feet and 2.5 inches and the average height of the rest of the group is 5 feet 10 inches

2. the sum of the heights of the n people is 178 feet and 9 inches

OA is A .

Could someone please explain why? Thanks
p.s. did try the search function but couldn't find this one...
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by GID09 » Thu Apr 02, 2009 1:34 pm
St 1 is Sufficient

To simplify, lets say average height of n/3 people is 1
and average height of rest i.e. 2n/3 is 2

Average height of n people = Total height/ n

= (n/3 *1 + 2n/3 * 2)/n = (5n/3)/n = gives you a value. Hence A.
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Re: Average height

by kanha81 » Mon Jun 15, 2009 9:36 am
Baldini wrote:What is the average height (arithmetic mean) of the n people in a certain group?

1. The average height of the n/3 tallest people in the group is 6 feet and 2.5 inches and the average height of the rest of the group is 5 feet 10 inches

2. the sum of the heights of the n people is 178 feet and 9 inches

OA is A .

Could someone please explain why? Thanks
p.s. did try the search function but couldn't find this one...
This is how I approached. Although, I got the answer right, let me know if the approach is correct or not.

AM = x / n = ?
where x = sum of the heights of n people
n = # of people

i) AM = 6 ft 2 1/2 inch = (n/3) / [n-(n/3)]
because n/3 is height of tallest people in the group and
n-(n/3) is subtracting the people having (n/3) height from the total number of people n

AM = 5 ft 10 inch = (2n/3) / [n - (2n/3)]
where 2n/3 is height of the rest of the tallest people in the group and
n-(2n/3) is subtracting the people having (2n/3) height from the totalk number of people.

Hence we have 2 equations and (i) is Suff.

ii) AM = 178 ft 9 inch / n
where n is total number of people.

Insuff

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