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 →

Probability

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 89
Joined: Thu Aug 26, 2010 9:29 am
Thanked: 4 times
by danjuma » Sun Oct 10, 2010 9:15 am
If 2 of the 4 expressions X + Y, X +5Y, X-Y, 5X-Y are chosen at random . What is the probability that their product will be of the form x square minus b( y square), where b is an integer?

a.1/2 b.1/3 c.1/6 d.1/5 e.1/4
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 268
Joined: Wed Mar 17, 2010 2:32 am
Thanked: 17 times

by this_time_i_will » Sun Oct 10, 2010 9:28 am
total number of possible outcome = 4c2 = 6
favorable outcome = 1. (selection of x+y and x-y)

so required probability = 1/6
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 9
Joined: Tue Aug 10, 2010 2:28 am

by NKB » Sun Oct 10, 2010 9:31 am
IMO right ans is C

only 2 pairs will give the required format i.e
1) X-Y & X +Y = X^2 - Y^2
2) X-5Y & X+5Y = X^2 -25Y^2

And in all there are 4 C 2 ways of selecting 2 pairs out of 4
Probability = 2/12 = 1/6
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1