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Can anyone explain this DS question for me? thanks

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Can anyone explain this DS question for me? thanks

by alwayslulu » Mon Mar 29, 2010 12:43 pm
I need an explanation of why stmt 1 alone is sufficient? Why not BOTH. Thanks! :)

~Lulu

During a certain college basketball game, the seniors on team A averaged 18 points and the non-seniors on team A averaged 12 points. What was the average (arithmetic mean) number of points scored per player on team A ?

(1) One-fourth of team A consisted of seniors.

(2) A total of 108 points were scored during the game.

Answer is: Stmt 1 is sufficient
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Source: — Data Sufficiency |
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by eaakbari » Mon Mar 29, 2010 1:10 pm
Stem

We need information about number of seniors or non seniors or total to form an equation

Statement one

Let total number be x

Therefore no of seniors = 1/4 *x
No of non seniors = 3/4*x

Hence total points
1/4*x*18 + 3/4*x*12
which is = 27x/2

For average we need to divide this my number of students which is x

Hence average is 27/2 Suff


Statement 2 - tells us nothing about strength of seniors or total etc

Hence answer is A
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by alwayslulu » Mon Mar 29, 2010 1:36 pm
Thank you for the quick response.

So can we find out what X is ? i know we don't have to solve the problem in DS question. But this will help me understand the problem. I'm still a bit confused.
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by eaakbari » Mon Mar 29, 2010 1:51 pm
In this question we do not have enough information to find out what x is, the only deduction we are able to make is the average

Since the average is defined as Sum of Data of n persons / n

If we have the numerator in terms of n we can cancel out with denominator, which is precisely what we have done in this question.
So do remember that to find average we need not require total number but a simple ratio or percentage sometimes suffices
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by alwayslulu » Mon Mar 29, 2010 2:08 pm
Got it!! ^-^

From the 1st statement, i cannot resolved what X is, but i can find the average by canceling the X from the numerator & the denominator.

However, if I used the second statement ... I can find what X is. X = 8. I know this step is not necessary. But it really helps me to understand the whole concept.

Thanks so much for your help!! :) I cannot wait to pass my GMAT exam and get it over with. :P
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