To find the average GPA

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To find the average GPA

by gmattesttaker2 » Sat Feb 08, 2014 7:40 pm
Hello,

Can you please tell me if my approach is correct here especially for Statement 2? Thanks a lot - Sri

At a certain high-school, the average GPA of female students is 3.2 and the average
GPA of male students is 3.0, what is the average GPA of the whole student body?

(1) The ratio of the number of female students to that of male students is 1.5:1.3.
(2) There are 530 male students at the school.


OA: A


My approach:

3.2 -----------x-----------3.0
f (3.2 -x) (x - 3) m


So, f/m = (x - 3)/(3.2 - x)

1) f/m = 1.5/1.3 = 15/13

=> (x - 3)/(3.2 - x) = 15/13

=> 13(x - 3) = 15(3.2 - x)

=> x = 87/28

Hence, Suff.


2) From the question we have,

f/m = (x - 3)/(3.2 - x)

Given, m = 530

So, f/m = (x - 3)/(3.2 - x) = ?/530

We don't have the number of females. Hence, in-sufficient.
Source: — Data Sufficiency |

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by Bill@VeritasPrep » Sat Feb 08, 2014 8:06 pm
Looks good. Of course, with Statement 1, you don't have to do all of the work; as soon as you realize you will get a definite value, you're done.

Statement 2 could also be disproven with some quick examples. If there are also 530 female students, the average is 3.1, but if there are 1,000 female students, the average will skew closer to 3.2. We can't get an exact value, so it is insufficient.
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by GMATGuruNY » Mon Feb 10, 2014 4:11 am
gmattesttaker2 wrote:Hello,

Can you please tell me if my approach is correct here especially for Statement 2? Thanks a lot - Sri

At a certain high-school, the average GPA of female students is 3.2 and the average
GPA of male students is 3.0, what is the average GPA of the whole student body?

(1) The ratio of the number of female students to that of male students is 1.5:1.3.
(2) There are 530 male students at the school.
What is the source of this problem?
The two statements contradict each other.
Statement 1: f/m = 15/13
Statement 2: m = 530
If f/m = 15/13 and m = 530, we get:
15/13 = f/530
f = 611.538.
This result is not viable, since the number of female students must be an integer.
In an actual GMAT DS problem, the two statements will NEVER offer contradictory information.
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