Data Sufficiency Question : Average

Expert replies

kfat: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Wed Nov 25, 2009 7:13 pm

by kfat » Mon Jul 12, 2010 3:58 pm

The average height of a group of children is 125 cm. If one of the children leaves, the average height drops by 2 cm. how many kids were there originally?
(1) The height of the child who left is twice greater than the height of the shortest child.
(2) The height of the child who left is 130 cm.

Like this post

Source: Beat The GMAT — Data Sufficiency | Mon Jul 12, 2010 3:58 pm

boazkhan: Master | Next Rank: 500 Posts; Posts: 135; Joined: Tue Oct 13, 2009 10:27 am; Thanked: 3 times

by boazkhan » Mon Jul 12, 2010 4:08 pm

IMO A. what is the OA?

Like this post

barcebal: Senior | Next Rank: 100 Posts; Posts: 81; Joined: Wed Jul 07, 2010 2:21 pmFollowed by: 2 members; Thanked: 12 times; GMAT Score:760

by barcebal » Mon Jul 12, 2010 8:05 pm

I want to say B but something isn't right.

n=number of original kids

(123*(n-1) + 130)/n = 125 right?

Simplified you get 125n = 123n -123 + 130

Simplify again and you 2n = 7

N=7/2

You can't have 7/2 kids. We get a value but we don't get a real answer? Are you sure the numbers are right?

Statement I seems not sufficient too. You can't really use the info about the smallest kid to infer how many kids there are and write an equation like I did in Statement B because we don't know how the smallest kid affects the avg.

Like this post

gmatmachoman: Legendary Member; Posts: 2326; Joined: Mon Jul 28, 2008 3:54 amFollowed by: 2 members; Thanked: 173 times; GMAT Score:710

by gmatmachoman » Mon Jul 12, 2010 11:40 pm

kfat wrote:The average height of a group of children is 125 cm. If one of the children leaves, the average height drops by 2 cm. how many kids were there originally?
(1) The height of the child who left is twice greater than the height of the shortest child.
(2) The height of the child who left is 130 cm.

St 2 should be sufficient. But the numbers are contradictory...

R&D on GMAT algorithm:

https://www.beatthegmat.com/r-d-on-gmat- ... tml#305739

Like this post

kfat: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Wed Nov 25, 2009 7:13 pm

by kfat » Tue Jul 13, 2010 7:26 am

Guys... The questions and figures in the questions both are correct. This problem was in 700-800 toughness level. Many a times persons sees a linear equation and marks the answer.

The answer for this question is "E". Person needs to solve to get n = 7/2 to avoid marking answer as "B".

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 » Tue Jul 13, 2010 8:55 am

kfat wrote:Guys... The questions and figures in the questions both are correct. This problem was in 700-800 toughness level. Many a times persons sees a linear equation and marks the answer.

The answer for this question is "E". Person needs to solve to get n = 7/2 to avoid marking answer as "B".

This question would never appear on the GMAT. The GMAT writers will never suggest an equation that results in 7/2 of a person.

(The justification for answer choice E seems to be that when you use the information given, you get 7/2 of a person, and since this number makes no sense, the statement is insufficient. You'll never face this situation on the GMAT.)

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

barcebal: Senior | Next Rank: 100 Posts; Posts: 81; Joined: Wed Jul 07, 2010 2:21 pmFollowed by: 2 members; Thanked: 12 times; GMAT Score:760

by barcebal » Tue Jul 13, 2010 9:14 am

kfat wrote:Guys... The questions and figures in the questions both are correct. This problem was in 700-800 toughness level. Many a times persons sees a linear equation and marks the answer.

The answer for this question is "E". Person needs to solve to get n = 7/2 to avoid marking answer as "B".

I agree with GMATguruNY,

The information in the question is inherently true and so is each statement. So if the facts given in the question are TRUE and statement 2 is TRUE (I'm not saying sufficient, I'm saying TRUE) then you get n = 7/2, which cannot answer the question, NOT BECAUSE statement 2 is unsufficient, but because either (A) the question's facts are incorrect or (B) statement 2 is false, both of which CAN NOT occur because we're not being tested on whether the statement is true, but rather sufficient.

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