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

Redeem

Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

★★★★★5.0559 reviews
GMATLiveTeach 7 seats left
Chris Peckover
NEXT LIVE COHORT

Oct 13 to Jan 7, 2027

with Chris Peckover

Schedule
Tue, Thu · 8:00 to 10:00 PM ET
Included
40 live hours + 6 months of GMAT OnDemand
  • Live instruction and real-time questions
  • Class recordings and assigned practice
View class & enroll
Limited cohort · enrollment openTarget Test Prep
EALiveTeach 5 seats left
Logan Thompson
EXECUTIVE ASSESSMENT

Sep 6 to Dec 6, 2026

with Logan Thompson

Schedule
Sun · 9:30 AM to 12:30 PM ET
Included
Live EA class + 6 months of EA OnDemand
  • Expert-led weekly online sessions
  • EA Masterclass access between classes
View EA class & enroll
Limited cohort · enrollment openTarget Test Prep
GMATOnDemand Start anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

130-point score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 559 reviewsTarget Test Prep

Compare the format, schedule, and included access before enrolling. Prices and seat counts shown reflect the supplied offer details.

Combination: differences

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 122
Joined: Fri May 22, 2009 10:38 pm
Thanked: 8 times
GMAT Score:700

by rah_pandey » Mon Jun 15, 2009 7:59 am
Are you sure according to me it should be 19.
by differences you mean (x-y) where x,y belong to {2,3,5,10,15}
in any case no of differences cannot be greater than (5c2)*(2!)+1
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

Re: Combination: differences

by Stuart@KaplanGMAT » Mon Jun 15, 2009 11:33 am
Naruto wrote:How many different differences can be obtained by taking 2 numbers at a time from 2,3,5,10 and 15

A 49
B 1898
C 1440
D 4320
E 720

Please double check the question - as written, the answer should be 18.

(5 numbers can be chosen first, 4 numbers can be chosen second, so there are 5*4 = 20 differences; however, 15-10 gives the same result as 10-5 and 5-10 gives the same result as 10-15, so we have to subtract the two duplicates.)
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
Master | Next Rank: 500 Posts
Posts: 122
Joined: Fri May 22, 2009 10:38 pm
Thanked: 8 times
GMAT Score:700

by rah_pandey » Mon Jun 15, 2009 7:38 pm
I think difference of a no from itself can also be taken as part of the soln that makes it 18+1=19
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 752
Joined: Sun May 17, 2009 11:04 pm
Location: Tokyo
Thanked: 81 times
GMAT Score:680

by tohellandback » Mon Jun 15, 2009 10:21 pm
according to me its 19
the differences are:

(2,2),(2,3),(2,5),(2,10),(2,15),(3,5),(3,10),(3,15),(5,10),(5,15),(3,2),(5,2),(10,2)(15,2),(5,3),(10,3),(15,3),(10,5),(15,5)
The powers of two are bloody impolite!!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 121
Joined: Thu Jun 11, 2009 1:16 am
Thanked: 4 times
GMAT Score:720

by Naruto » Mon Jun 15, 2009 10:38 pm
Yes even my answer was 19, I was wondering if i was reading the question wrong or something, am sorry guys I got this question from one of the online prep tests and i guess they are no good and have wrong answers. I'll be more careful of my posts henceforth.

:oops:
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1