dabaobao wrote:

Bunuel wrote:

Of the 800 employees of Company X, 70 percent have been with the company for at least ten years. If y of these "long-term" members were to retire and no other employee changes were to occur, what value of y would reduce the percent of "long-term" employees in the company to 60 percent ?

A. 200

B. 160

C. 112

D. 80

E. 56

The # of "long-term" employees is 70%*800=560.

After y of them retire new # of "long-term" employees would become 560-y.

Total # of employees would become 800-y.

We want 560-y to be 60% of 800-y --> 560-y=(800 -y)*60% --> y = 200.

Answer: A.

VeritasKarishma Bunuel I'm trying to use weighted averages for this Q, but I'm getting a different answer. Could you please tell me what am I doing wrong below? Thanks!

People leaving = Pulling the average to 0% => Use 0% for them. Similar to the way how we

~~remove~~replace/add an ingredient from a mixture, we take it as 0% or 100% respectively. Example:

https://gmatclub.com/forum/a-bag-contai ... ml?kudos=1 6:1

0% ------------60%--70%

Left New Avg Old Avg

# of long term employees: 7/10 * 800 = 560

Left = 1/7 * 560 = 80 => One of the answer choices.

or

Left = 1/7 * 800 = Not an int!

I guess this would the correct answer if we were not just "reducing" but instead "replacing" y long term people. So that's my problem? In the beans/pulses example Q, we replace beans with pulses, and that's why we take the weighted average between 0% (after replacement) and 40% (original concentration), something that we can't do here since we're "reducing" and not "replacing". Even if we were replacing in this Q, I guess we would need to use 800 and not 560 for the total mixture?

You can use weighted average here but you have to be very clear about which 2 groups are getting together (or splitting apart) to give you an average group.

Group 1 + Group 2 = Avg Group

If, as per your logic, Group 1 has 70% concentration of long term employees (the total group of 800)

and Group 2 has 0% concentration of long term amp which means this is made of only short term employees - how many people are in this group?

Do the 2 groups combine to give the avg 60% group? No.

This is what the scene is - There is a group 1 which consists of 60% long term employees.

There is a group 2 which consists of all long term employees (that are removed) so concentration of long term employees = 100%

Together these two groups combined to form the 70% concentration group of 800 people (and now we are splitting them).

w1/w2 = (A2 - Avg)/(Avg - A1) = (100 - 70)/(70 - 60) = 3/1

So w2 = 1/4 of total = (1/4) * 800 = 200 = Number of people in group 2 = y

Answer (A)

_________________

Karishma

Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >