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 →

If a equals the sum of the even integers...

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Master | Next Rank: 500 Posts
Posts: 253
Joined: Fri Dec 26, 2008 8:39 pmFollowed by: 1 member
Thanked: 8 times
by BlindVision » Wed Jun 17, 2009 10:56 am
If a equals the sum of the even integers from 2 to 20, inclusive, and b equals the sum of the odd integers from 1 to 19, inclusive, what is the value of a - b ?

A) 1

B) 10

C) 19

D) 20

E) 21


OA = B
Life is a Test
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 472
Joined: Sun Mar 29, 2009 6:54 pm
Thanked: 56 times

by ssmiles08 » Wed Jun 17, 2009 12:09 pm
some formulas you might want to remember to make your calculations easier:

# of integers: (highest multiple - lowest multiple)/increment + 1

average of evenly spaced sets: (highest + lowest)/2

now:

even numbers:

(20-2)/2 + 1 = 10 even integers.
(20+2)/2 = 11 is the average of the even set.
sum = avg*(#of elements) = 11*10 = 110 = a


odd numbers:
(19-1)/2 + 1 = 10 odd integers.
(19+1)/2 = 10 is the average of the odd set.
sum = avg*(#of elements) = 10*10 = 100 = b

a-b = 110 - 100 = 10. (B)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 103
Joined: Mon May 18, 2009 9:47 am
Thanked: 19 times

by raleigh » Thu Jun 18, 2009 9:45 am
ssmiles approach is the quickest for these types of problems. If you don't feel comfortable with the formulas/approach, check out Manhattan GMAT's Number Properties book. It's a great book.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 613
Joined: Thu Mar 22, 2007 6:17 amFollowed by: 64 members
Location: madrid
Thanked: 171 times
GMAT Score:790

Re: If a equals the sum of the even integers...

by kevincanspain » Thu Jun 18, 2009 1:19 pm
BlindVision wrote:If a equals the sum of the even integers from 2 to 20, inclusive, and b equals the sum of the odd integers from 1 to 19, inclusive, what is the value of a - b ?

A) 1

B) 10

C) 19

D) 20

E) 21

a - b = (20-19) + (18-17) + ... + (2 - 1) = 10

OA = B
Kevin Armstrong
GMAT Instructor
Gmatclasses
Madrid
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1