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GMAT PREP Q

by Lifetron » Sat Apr 27, 2013 1:34 am
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 employees?

(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
Weighted Average Solution : https://www.beatthegmat.com/mba/2009/12/ ... art-1-of-2
I solved this using Alligation
Which method is the best one ?[/spoiler]

Experts pls help !
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by Anju@Gurome » Sat Apr 27, 2013 1:53 am
gughanbose wrote: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 employees?

(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.
Let us assume the number of male employees in the company is m and number of female employees is f. Average number of years of experience for male employees is 9.8 and average number of years of experience for female employees is 9.1.
We need the ratio m:f.

Statement 1: m = 52
This is not enough to determine the ratio of m:f.

Not sufficient.

Statement 2: (9.8m + 9.1f)/(m + f) = 9.3
--> 9.8m + 9.1f = 9.3m + 9.3f.
--> 0.5m = 0.2f
--> m/f = m : f = 2:5

Sufficient

The correct answer is B.
gughanbose wrote:Which method is the best one ?
Weighted average and alligation are often the same method under different names and explained a bit differently. When they are actually different, both have their advantages and disadvantages.

It is you who should choose the method which works for you the best.
As usual my suggestion is do not to stick to one particular method. That way you'll end up sticking to a method which works best for a particular problem but not so good (often fails) for other problems on the same concept. Most of the problems in GMAT can be solved in more than method. Solve any problem with as much methods as you can. Only then you'll learn the trick of always identifying the best method.

For example, for this the best method that works for me is : if I know the weighted average of two quantity A and B, and the values of A and B, I can find out the ratio of the weights of A and B. So, as soon as I read the statement 2, I know it is sufficient. No algebra, no calculation, nothing. I'll just read the statement, mark the answer, and move on.

But others may not find this as the best method as they may not know "What is weighted average?" or "How can one conclude that?".
Anju Agarwal
Quant Expert, Gurome

Backup Methods : General guide on plugging, estimation etc.
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by GMATGuruNY » Sat Apr 27, 2013 2:51 am
gughanbose wrote: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 employees?

(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.
This is a WEIGHTED AVERAGE/MIXTURE problem.
Average for the men = 9.8.
Average for the women = 9.1.

If the average for the MIXTURE of men and women is known, ALLIGATION can be used to determine the RATIO of men to women.
Check here to see how alligation can be used to determine the ratio of ingredients in a mixture:
https://www.beatthegmat.com/ratios-fract ... tml#484583
https://www.beatthegmat.com/a-charitable ... 88187.html
https://www.beatthegmat.com/mixture-prob ... tml#604126
https://www.beatthegmat.com/mixture-prob ... 90121.html
https://www.beatthegmat.com/algebra-t195034.html
https://www.beatthegmat.com/mixture-prob ... 18206.html

Question stem rephrased: What is the average for the mixture of men and women?

Statement 1: There are 52 male employees at the company.
INSUFFICIENT.

Statement 2: The average number of years of experience for the company's male and female employees combined is 9.3 years.
SUFFICIENT.

The correct answer is B.
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