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What is the average --- a doubt

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What is the average --- a doubt

by atulmangal » Sun May 01, 2011 2:50 pm
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 2.5 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

This question is easy but i have one doubt...

Do i take question in this way that Av height which we have to find out should not contain "n" as an expression...or if the Av. ht contain "n" then thats okay??? In sum. answer containing "n" is okay or not???

I know this doubt is silly but this may appear in my mind in exam so better to get rid of this right now...
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by parkman » Sun May 01, 2011 3:35 pm
My basic approach to DS is the MGMAT apporach

1. Is it a y/n or value question?
2. This would be a value, so does (1) give us the information to get a value?

A value to me always means a specific number, because we can almost always create an equation containing unknown values out of the information given in the original question.

Like if a question is:
Company X has a total of Y number of employees that make $10,000 a year. What is Company X's payroll?
We can certainly answer this with an equation, ($10,000)Y , but that is not enough to answer the question
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by atulmangal » Sun May 01, 2011 3:42 pm
parkman wrote:My basic approach to DS is the MGMAT apporach

1. Is it a y/n or value question?
2. This would be a value, so does (1) give us the information to get a value?

A value to me always means a specific number, because we can almost always create an equation containing unknown values out of the information given in the original question.

Like if a question is:
Company X has a total of Y number of employees that make $10,000 a year. What is Company X's payroll?
We can certainly answer this with an equation, ($10,000)Y , but that is not enough to answer the question
Thanks bro i got your point...
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by champmag » Sun May 01, 2011 11:02 pm
Atul,

Whenever there is a variable specified in the question, unless the question demands that the value is to be found in the terms of the variable, the value needs to be a specific number.

In the above question, option A gives a specific number whereas option B gives the avg. height as Total height/n; Since, n is variable the avg. height will vary according to the value of n and so the statement is not sufficient to provide a specific answer.

Thus eliminate B. OA is A.
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by Ian Stewart » Mon May 02, 2011 9:49 am
In DS questions, if you are asked to find the value of something, you *only* have sufficient information if you can find one (and only one) *numerical* value. If you can only find the value in terms of some letter n, you don't have enough information.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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by atulmangal » Mon May 02, 2011 11:33 am
Ian Stewart wrote:In DS questions, if you are asked to find the value of something, you *only* have sufficient information if you can find one (and only one) *numerical* value. If you can only find the value in terms of some letter n, you don't have enough information.
Yup, got your point Ian..Thanks a lot
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