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ratios + weighted average

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ratios + weighted average

by cramya » Sat Oct 25, 2008 1:00 pm
At a certain company, the average (arithmetic mean) number of years of experience is 9.8 years for the male employees and 9.1 years for the female employees. What is the ratio of the number of the company's male employees to the number of the company's female employee?

(1) There are 52 male employees at the company
(2) The average number of years of experience for the company's male and female employees combined is 9.3 years.



[spoiler]OA: B[/spoiler]

My question is how is the number of ears of service related to the number of males/females. Lets sa the average ears of experience of females
is 10 (there could be 2 females wiht 5 earsof experiecne each or 5 females with 2 ears of experience each) The ratio fo males to females changes.

Wh is not E)? Can someone please clear m confusion?
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Source: — Data Sufficiency |
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by cramya » Sat Oct 25, 2008 1:02 pm
The y key stopped responding on my key board so reposting the same question!



At a certain company, the average (arithmetic mean) number of years of experience is 9.8 years for the male employees and 9.1 years for the female employees. What is the ratio of the number of the company's male employees to the number of the company's female employee?

(1) There are 52 male employees at the company
(2) The average number of years of experience for the company's male and female employees combined is 9.3 years.



[spoiler]OA: B [/spoiler]
My question is how is the number of years of service related to the number of males/females. Lets sa the average ears of experience of females
is 10 (there could be 2 females wiht 5 earsof experiecne each or 5 females with 2 ears of experience each) The ratio fo males to females changes.

Why is not E)? Can someone please clear my confusion?
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by cramya » Sat Oct 25, 2008 4:09 pm
Sorry for the confusion

I figured it out!
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by Ian Stewart » Sat Oct 25, 2008 5:15 pm
About weighted averages, I'd just add that in any weighted average problem involving two groups, if you have any three of the following, you can always find the fourth:

-the average of group 1 (men, in the question above)
-the average of group 2 (women, in the question above)
-the overall average (all employees, in the question above)
-the ratio of group 1 to group 2 (ratio of male to female employees in the above)

This can be quite useful to know for DS questions; it lets you solve the above problem in a few seconds, since with Statement 2 we have three of the four items above, so can find the fourth, and Statement 1 is clearly insufficient.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
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by cramya » Sat Oct 25, 2008 6:12 pm
Thanks Ian!!
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by California4jx » Sat Jun 27, 2009 9:27 am
The average of averages =
Sum of experiences of both groups / total employees

9.3 = (M)(9.8) +(F)(9.1) / (M + F)

from there - you can find M/F
Sufficient.
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