Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
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.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

ratio and proportion

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 8
Joined: Mon Dec 13, 2010 3:14 pm
by DJHJA » Mon Dec 13, 2010 9:49 pm
In a class, 10% of the girls have blue eyes, and 20% of the boys have blue eyes.
If the ratio of girls to boys in the class is 3:4, then what is the fraction of students in the class having blues eyes?


the answer is 11/70, however the solution given is;

let 1 represent the total # of students
1-(.1+.2)= .7 ( why is this done??? :? why isnt it .1+.2=.3 as the denominator)

girls(with blue eyes) + boys(with blue eyes) =
(3*.1 )+(4*.2)/ .7 = .3+.8/.7= .11/.7 = 11/70

why is .7 the denominator and not .3.
isnt .3 the total percentage of students with blue eyes?
Top
Join the discussion
Source: — Problem Solving |
Legendary Member
Posts: 1337
Joined: Sat Dec 27, 2008 6:29 pmFollowed by: 10 members
Thanked: 127 times

by Night reader » Mon Dec 13, 2010 10:07 pm
DJHJA wrote:In a class, 10% of the girls have blue eyes, and 20% of the boys have blue eyes.
If the ratio of girls to boys in the class is 3:4, then what is the fraction of students in the class having blues eyes?


the answer is 11/70, however the solution given is;

let 1 represent the total # of students
1-(.1+.2)= .7 ( why is this done??? :? why isnt it .1+.2=.3 as the denominator)

girls(with blue eyes) + boys(with blue eyes) =
(3*.1 )+(4*.2)/ .7 = .3+.8/.7= .11/.7 = 11/70

why is .7 the denominator and not .3.
isnt .3 the total percentage of students with blue eyes?
girls/boys=3/4 => girls/total=3/7 & boys/total=4/7 <=> 3/7 + 4/7 = 1 (girls+boys over total)

blue eyed boys 20% or 1/5
blue eyed girls 10% or 1/10

how many of all boys are blue eyed => 1/5 * 4/7 = 4/35
how many of all girls are blue eyed => 1/10 * 3/7 = 3/70

how many of all boys and girls are blue eyed => 4/35 + 3/70 = 11/70

many OA explanations may differ in notation and decimal translations; we need to know the method only
Top
Join the discussion
Newbie | Next Rank: 10 Posts
Posts: 8
Joined: Mon Dec 13, 2010 3:14 pm

by DJHJA » Mon Dec 13, 2010 10:23 pm
omg thanks ur a life saver
Top
Join the discussion
Legendary Member
Posts: 537
Joined: Fri Jan 22, 2010 10:06 pmFollowed by: 1 member
Thanked: 14 times

by frank1 » Tue Dec 14, 2010 1:00 am
When you see two set of mutually exclusive sets use this method...
it saves time
Image
11/70 clear from it
GMAT score is equally counted as your GPA and 78 clicks can change you life.
Top
Join the discussion
User avatar
Master | Next Rank: 500 Posts
Posts: 181
Joined: Fri Sep 04, 2009 12:06 pmFollowed by: 1 member
Thanked: 17 times

by ikaplan » Tue Dec 14, 2010 7:22 am
Double matrix method is one of the most useful techniques I have learned during the GMAT prep period. Frank1, thanks for reminding us to use it!
"Commitment is more than just wishing for the right conditions. Commitment is working with what you have."
Top
Join the discussion