Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

What is the average (arithmetic mean) height of the n people [#permalink]
14 Jul 2010, 12:35

1

This post received KUDOS

2

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

25% (medium)

Question Stats:

65% (01:48) correct
35% (00:50) wrong based on 181 sessions

What is the average (arithmetic mean) height 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 people in the group is 5 feet 10 inches (2) the sum of the heights of the n people is 178 feet 9 inches

what is the average (arithmetic mean) height 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 people in the group is 5 feet 10 inches

(2) the sum of the heights of the n people is 178 feet 9 inches

pranrasvij wrote:

zisis wrote:

pranrasvij wrote:

A is easily the right choice since it gives info about the rest (1-n/3) and n/3 => we dont need the final value of "n" in that case.

B gives us total height but no way to get the mean without more on "n".

so the mean height is the heights given at a ration 1:2 ????

please explain....

yep... all you have to do is the add the 2 heights and divide by 2 to get the mean height => easy to calculate (IMHO!)

Answer to the question is A, but you shouldn't divide the "sum" by 2, you should divide by n.

Weighted \ average=\frac{sum \ of \ weights}{# \ of \ data \ points}, or in our case average \ height=\frac{sum \ of \ heights}{# \ of \ people}.

(1) The average height of \frac{n}{3} people is 74.5 inches and the average height of \frac{2n}{3} people (the res of the people in the group n-\frac{n}{3}=\frac{2n}{3}) is 70 inches --> average \ height=\frac{sum \ of \ heights}{# \ of \ people}=\frac{74.5*\frac{n}{3}+70*\frac{2n}{3}}{n} --> n cancels out --> average \ height=74.5*\frac{1}{3}+70*\frac{2}{3}. Sufficient.

(2) Sum of heights equals to 178 feet 9 inches --> only nominator is given. Not sufficient.

Bunel - I need one help. This is not a difficult question and it's easy to see that A is sufficient. However I thought B is suf too because the stimulus says N. Now N could be anything. Is it not sufficient to say avg height = sum of heights (given in the second option)/N - N is mentioned in the stem. Why do we have to concern with the actual value of N?

Bunel - I need one help. This is not a difficult question and it's easy to see that A is sufficient. However I thought B is suf too because the stimulus says N. Now N could be anything. Is it not sufficient to say avg height = sum of heights (given in the second option)/N - N is mentioned in the stem. Why do we have to concern with the actual value of N?

Official Guide:

In data sufficiency problems that ask for the value of a quantity, the data given in the statements are sufficient only when it is possible to determine exactly one numerical value for the quantity.

(1) The average height of \frac{n}{3} people is 74.5 inches and the average height of \frac{2n}{3} people (the res of the people in the group n-\frac{n}{3}=\frac{2n}{3}) is 70 inches --> average \ height=\frac{sum \ of \ heights}{# \ of \ people}=\frac{74.5*\frac{n}{3}+70*\frac{2n}{3}}{n} --> n cancels out --> average \ height=74.5*\frac{1}{3}+70*\frac{2}{3}. Sufficient.

(2) Sum of heights equals to 178 feet 9 inches --> only nominator is given. Not sufficient.

Answer: A.

Hope it helps.

Hi Bunuel, The fact that confused me is the word tallest in statement 1. It says "average height of n/3 [highlight]tallest[/highlight] people in the group is 6 feet 2.5 inches.

Isn't this bit ambiguous? We have no clue how many people to consider in tallest category?

(1) The average height of \frac{n}{3} people is 74.5 inches and the average height of \frac{2n}{3} people (the res of the people in the group n-\frac{n}{3}=\frac{2n}{3}) is 70 inches --> average \ height=\frac{sum \ of \ heights}{# \ of \ people}=\frac{74.5*\frac{n}{3}+70*\frac{2n}{3}}{n} --> n cancels out --> average \ height=74.5*\frac{1}{3}+70*\frac{2}{3}. Sufficient.

(2) Sum of heights equals to 178 feet 9 inches --> only nominator is given. Not sufficient.

Answer: A.

Hope it helps.

Hi Bunuel, The fact that confused me is the word tallest in statement 1. It says "average height of n/3 [highlight]tallest[/highlight] people in the group is 6 feet 2.5 inches.

Isn't this bit ambiguous? We have no clue how many people to consider in tallest category?

It means that if we order these n people from shortest to tallest and consider \frac{n}{3} tallest people, then their average height would be 74.5 feet. _________________

Re: What is the average (arithmetic mean) height of the n people [#permalink]
03 Aug 2014, 18:03

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________