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 →

OG 2016 DATA Sufficiency #135

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members
Location: Palo Alto, CA
Thanked: 2867 times
GMAT Score:800

by [email protected] » Sat Dec 26, 2015 10:19 am
Hi AshB,

When posting questions in the Forums, you should post the entire question.

For this particular prompt, you should also explain why you disagree with the solution.

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 7
Joined: Mon Jul 27, 2015 4:52 am
Thanked: 1 times

by AshB » Sat Dec 26, 2015 3:02 pm
A list contains 3 different numbers. Does the median of the 3 numbers equal the average(arithmetic mean) of the 3 numbers?
1) The range of 3 numbers is equal to twice the difference between the greatest number and the median
2) The sum of the 3 numbers is equal to 3 times one of the numbers

OG solves 2) by deriving that all the 3 numbers in the list are equal, which contradicts the question stem information: "different numbers"? Does this happen often on GMAT?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
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 » Sat Dec 26, 2015 4:21 pm
AshB wrote:A list contains 3 different numbers. Does the median of the 3 numbers equal the average(arithmetic mean) of the 3 numbers?
1) The range of 3 numbers is equal to twice the difference between the greatest number and the median
2) The sum of the 3 numbers is equal to 3 times one of the numbers
When numbers are EVENLY SPACED, the median is equal to the average.
Question stem, rephrased:
Are the 3 numbers evenly spaced?

Statement 1:
Let the 3 numbers, in ascending order, be a, b and c.
Range = biggest - smallest = c-a.
Difference between the greatest number and the median = c-b.

Since the range is equal to twice the difference between the greatest number and the median, we get:
c-a = 2(c-b)
c-a = 2c - 2b
2b = a + c
b = (a+c)/2.

Since b is equal to the average of a and c, b must be HALFWAY between a and c, implying that a, b and c are EVENLY SPACED.
SUFFICIENT.

Statement 2:
Case 1: One of the numbers is 1.
If the sum is equal to three times 1, then the sum is equal to 3.
Options for the 3 numbers:
0, 1, 2 --> 0+1+2 = 3.
-1, 1, 3 --> -1+1+3 = 3
-10, 1, 12 --> -10+1+12 = 3.
In every case, the 3 numbers are EVENLY SPACED.

Case 2: One of the numbers is 10.
If the sum is equal to three times 10, then the sum is equal to 30.
Options for the 3 numbers:
9, 10, 11 --> 9+10+11 = 30.
0, 10, 20 --> 0+10+20 = 30.
-10, 10, 30 --> -10+10+30 = 30.
In every case, the 3 numbers are EVENLY SPACED.

As Cases 1 and 2 illustrate, for the sum to be equal to three times one of the numbers, the 3 numbers must be EVENLY SPACED.
SUFFICIENT.

The correct answer is D.
Last edited by GMATGuruNY on Sun Dec 27, 2015 10:36 pm, edited 1 time in total.
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
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
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 » Sat Dec 26, 2015 4:43 pm
AshB wrote:OG solves 2) by deriving that all the 3 numbers in the list are equal, which contradicts the question stem information: "different numbers"? Does this happen often on GMAT?
The OG's explanation for Statement 2 is faulty.
Since the prompt requires that the 3 numbers be DIFFERENT, the explanation for Statement 2 should not discuss cases in which the 3 numbers are EQUAL.
As my solution above shows, statement 2 can be satisfied by 3 different numbers.
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
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1