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 →

Sum of positive integers x and y

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 418
Joined: Sun Jul 04, 2010 12:48 pmFollowed by: 3 members
Thanked: 6 times
by gmatdriller » Sat Jul 23, 2011 12:47 am
The sum of positive integers x and y is 77. What is the value of xy?

(i) x = y + 1
(ii) x and y have the same tens digit
suggest an efficient algebraic method.

Thanks
SOURCE: GMATPREP1

OA: D
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Data Sufficiency |
User avatar
Legendary Member
Posts: 1309
Joined: Mon Apr 04, 2011 5:34 amFollowed by: 123 members
Location: India
Thanked: 310 times
GMAT Score:750

by cans » Sat Jul 23, 2011 12:54 am
x+y=77
a) x= y+1. get one x and one y and thus xy is unique
Sufficient
b) x and y have same 10 digits. so it must be 3. (if 2, then max sum can be 58 and if 4, then min sum can be 80)
as sum is 77, it means the sum of unit places is 17. and that's possible only with 8 and 9 (9+8=17)
thus no.s are 38,39
unique product.
Sufficient
IMO D
If my post helped you- let me know by pushing the thanks button ;)

Contact me about long distance tutoring!
[email protected]

Cans!!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 759
Joined: Mon Apr 26, 2010 10:15 amFollowed by: 3 members
Thanked: 85 times

by clock60 » Sat Jul 23, 2011 1:25 am
one more way to solve st 2, but in essence the same as that of can
x=10a+b
y=10a+m. where a is the same tens digit for x and y and b and m are digits
10a+b+10a+m=77
20a+b+m=77, here a can`t 4 as 20*4=80 that is more than 77, and here a can`t 2 as 20*2=40, and themax value of m+b=18, (40+18=56<77)
so the only value for a is 3
60+b+m=77
b+m=17, the only values for b and m are 9 and 8 so given x and y are 39, and 38 possible to find their product
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 418
Joined: Sun Jul 04, 2010 12:48 pmFollowed by: 3 members
Thanked: 6 times

by gmatdriller » Sun Jul 24, 2011 12:49 am
Your contributions make sense; thanks "cans" and "clock60"
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1