BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

Interesting Set problem - Gmat800

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
Newbie | Next Rank: 10 Posts
Posts: 9
Joined: Wed May 07, 2008 7:47 pm
Thanked: 1 times

answer -> a?

by kbm1975 » Thu May 08, 2008 5:34 pm
in case
set X={1,4,5,6}
set Y={-1,4,5,6}

(1) no -> sufficient from set X
(2) no(from set X), yes(from set Y) -> insufficinet

therefore A

Is it right?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 343
Joined: Mon Jan 21, 2008 3:28 pm
Thanked: 4 times

by arorag » Thu May 08, 2008 6:20 pm
Ans should be A. B is not giving anything abt the sign of nos
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 3225
Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members
Location: Toronto
Thanked: 1710 times
GMAT Score:800

by Stuart@KaplanGMAT » Thu May 08, 2008 7:06 pm
Just a quick note:

(1) is not sufficient alone.

The range of {1, 4, 14} is 13. Adding 13 to the set doesn't increase the range.

The range of {50, 51, 63} is 13. Adding 13 to the set does increase the range.

We can get both a yes and a no, insufficient.
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 631
Joined: Mon Feb 18, 2008 11:57 pmFollowed by: 3 members
Thanked: 29 times

by netigen » Thu May 08, 2008 7:40 pm
OA is C
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 631
Joined: Mon Feb 18, 2008 11:57 pmFollowed by: 3 members
Thanked: 29 times

by netigen » Mon May 12, 2008 2:35 pm
This is the solution I found for this Q

1. A is insufficient for the reason noted by Stuart above
2. Lets look at option 2

Avg of set A(n) = Total of Set A(n) / n (assuming n=numbers in set A)

Avg of set A(n+1) = Total of Set A(n) + R/ (n+1) < R

Total of Set A(n) + R < R (n+1)

Total of Set A(n) + R < Rn + R

or Total of Set A(n) / n < R

which means that Avg of set A(n) < R

This means that there are number less than and greater than R in the A hence the range will not increase by addition of R hence the ans C
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 29
Joined: Wed Feb 27, 2008 4:56 am
Thanked: 2 times

by ricaototti » Tue Sep 02, 2008 9:54 pm
I am sorry but I really dont get it why it should be C.
I think it should be E.
I understand why 1 and 2 are wrong... but not why C is correct. Please, can someone explain it better.

Thanks
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 124
Joined: Mon May 19, 2008 1:12 pm
Thanked: 3 times

by Nycgrl » Tue Sep 02, 2008 10:02 pm
It should be E...what's OA?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 891
Joined: Sat Aug 16, 2008 4:21 amFollowed by: 1 member
Thanked: 27 times
GMAT Score:660(

by 4meonly » Wed Sep 03, 2008 10:38 am
E agree
Waiting for OA
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1153
Joined: Wed Jun 20, 2007 6:21 amFollowed by: 2 members
Thanked: 146 times

Re: Interesting Set problem - Gmat800

by parallel_chase » Wed Sep 03, 2008 3:37 pm
netigen wrote:This is an interesting Range problem. I am trying to figure out the best approach to solve it
Clearly statement I and II alone are insufficient for the same reasons mentioned by Stuart.

Combining I & II

New number added = R

all the number in the set are positive
NEW MEAN of the set with NEW NUMBER added is less than R.

4,4,4
range = 0
mean = 4

new number= 0
0,4,4,4
mean=3
range=4

Range increased from 0 to 4

2,4,8
range=6

new number=6
2,4,6,8
mean=5
range=6

range remains the same.

Hence E.

I dont know how OA can be C, or am i missing something.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members
Location: Montreal
Thanked: 1090 times
GMAT Score:780

by Ian Stewart » Wed Sep 03, 2008 3:54 pm
The range of a set A is R. A number having a value of R is added to set A. Will the range of set A increase?
1) All numbers in set A are positive.
2) The mean of the new set is smaller than R.

I think the above posts confirm that the answer is either C or E, so I won't bother looking at the statements individually. Let's look at both statements together.

When we add R to set A, the range will only increase if R is either the largest element in the new set, or the smallest element in the new set. We want to know if R could be the largest or the smallest element in the new set.

Let's assume A contains at least two elements, and call the largest g, and the smallest s. So set A is {s, other stuff, g}. Then R = g - s. From this, because g and s are positive, R must be less than g. So R can't be the largest element in the new set.

The only question is whether R might be the smallest; that is, we want to know if it's possible that R < s. This would make R smaller than everything else in the set, since s was the smallest element of the old set. But if R is the smallest element of the new set, there's no way statement 2 could be true; the mean of a set cannot be smaller than its smallest element. So R can neither be the smallest nor the largest element in the set, and the range of the new set must be equal to the range of the old set. Sufficient. C.
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
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members
Location: Montreal
Thanked: 1090 times
GMAT Score:780

Re: Interesting Set problem - Gmat800

by Ian Stewart » Wed Sep 03, 2008 3:59 pm
parallel_chase wrote:
New number added = R

all the number in the set are positive
NEW MEAN of the set with NEW NUMBER added is less than R.

4,4,4
range = 0
mean = 4

new number= 0
0,4,4,4
mean=3
range=4
You can't use this example; the mean of the new set is not less than R, the range of the first set, which is zero. This set thus doesn't conform with the information in Statement 2.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1