Need Explanation for a DS problem from OG'13

Expert replies

Digvijay01: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Mon Aug 29, 2011 6:04 amFollowed by: 4 members; Thanked: 3 times

by Digvijay01 » Wed Oct 23, 2013 12:52 pm

Hi can someone give me an explanation of why ans is "c" for this. I'm not satisfied with explanation in OG.

What is the median number of employees assigned per project for the projects at Company Z ?
(1) 25 percent of the projects at Company Z have 4 or more employees assigned to each project.
(2) 35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.

Like this post

Source: Beat The GMAT — Data Sufficiency | Wed Oct 23, 2013 12:52 pm

GMAT/MBA Expert

ceilidh.erickson: GMAT Instructor; Posts: 2095; Joined: Tue Dec 04, 2012 3:22 pmFollowed by: 247 members; Thanked: 1443 times

by ceilidh.erickson » Wed Oct 23, 2013 1:30 pm

If we want the median number of employees assigned when given percents, we effectively want the 50th percentile, which would be the middle value.

Statement 1 tells us about 25% of the projects, but we can't infer anything about the others. Insufficient.

Statement 2 tells us about 35% of the projects, but again we can't infer about the others. Insufficient.

If we put the statements together:
25% of projects have 4 or more employees
35% of projects have 2 or fewer
What's the only other possibility? Exactly 3 employees. Therefore, we can infer that 40% of the projects have exactly 3 employees. If we arrange this information in order:

0%-35% is 2 or fewer
35%-75% is exactly 3
75%-100% is 4 or more

The 50% mark occurs at exactly 3 employees, so that's the median.

Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education

Like this post

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Wed Oct 23, 2013 7:24 pm

I posted an explanation here:

https://www.beatthegmat.com/median-probl ... tml#681492

Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

Like this post

Uva@90: Master | Next Rank: 500 Posts; Posts: 490; Joined: Thu Jul 04, 2013 7:30 amFollowed by: 5 members; Location: Chennai, India; Thanked: 83 times

by Uva@90 » Wed Oct 23, 2013 8:33 pm

Digvijay01 wrote:Hi can someone give me an explanation of why ans is "c" for this. I'm not satisfied with explanation in OG.

What is the median number of employees assigned per project for the projects at Company Z ?
(1) 25 percent of the projects at Company Z have 4 or more employees assigned to each project.
(2) 35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.

Hi Digvijay01,

Firstly, how do we find the median ?
We will arrange all the number in ascending order and find the middle value.

Similarly we will approach this problem too,

arrange the project with number of employees with ascending order

0----1------------2----------------3-----------4---------------and goes on

Statement 1
25 percent of the projects at Company Z have 4 or more employees assigned to each project

so 25% have 4 or more employees

-------------------------------------------------4>----------

We dont know the rest 75 percent hence we cant decide,

Statement2
35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.

so 35% have 2 or less
---------------------<2--------------------------------------------------

Combining 1 and 2

-------------------<2--------------------------4>------------------------

so, middle 40% have number of employees as 3
hence median become 3. Hence sufficient
So answer is C

Hope it is clear to you now.

Regards,
Uva.

Known is a drop Unknown is an Ocean

Like this post

GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Wed Oct 23, 2013 8:56 pm

Digvijay01 wrote: What is the median number of employees assigned per project for the projects at Company Z?

(1) 25 percent of the projects at Company Z have 4 or more employees assigned to each project.
(2) 35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.

Target question: What is the median number of employees assigned per project?

Statement 1: 25 percent of the projects at Company Z have 4 or more employees assigned to each project.
Let's pretend that there are 4 projects altogether.
There are several sets of values that meet this condition. Here are two:
Case a: the set of numbers representing employees per project are {1, 1, 1, 4} in which case the median is 1
Case b: the set of numbers representing employees per project are {2, 2, 2, 4} in which case the median is 2
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 1: 35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.
Using logic similar to the above, we can show that statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined:
35% projects have 2 employees or fewer, and 25% of the projects have 4 employees or more. So, 40% projects have exactly 3 employees.

This tells us that the median must be 3.
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer = C

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

Digvijay01: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Mon Aug 29, 2011 6:04 amFollowed by: 4 members; Thanked: 3 times

by Digvijay01 » Wed Oct 30, 2013 3:09 am

Thanks much...!! It sure does helped... Number line figure helped me to get more clarity.. Cheers..

Uva@90 wrote:
Digvijay01 wrote:Hi can someone give me an explanation of why ans is "c" for this. I'm not satisfied with explanation in OG.

What is the median number of employees assigned per project for the projects at Company Z ?
(1) 25 percent of the projects at Company Z have 4 or more employees assigned to each project.
(2) 35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.
Hi Digvijay01,

Firstly, how do we find the median ?
We will arrange all the number in ascending order and find the middle value.

Similarly we will approach this problem too,

arrange the project with number of employees with ascending order

0----1------------2----------------3-----------4---------------and goes on

Statement 1
25 percent of the projects at Company Z have 4 or more employees assigned to each project

so 25% have 4 or more employees

-------------------------------------------------4>----------

We dont know the rest 75 percent hence we cant decide,

Statement2
35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.

so 35% have 2 or less
---------------------<2--------------------------------------------------

Combining 1 and 2

-------------------<2--------------------------4>------------------------

so, middle 40% have number of employees as 3
hence median become 3. Hence sufficient
So answer is C

Hope it is clear to you now.

Regards,
Uva.

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review