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 dose for the day

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 1560
Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members
Thanked: 137 times
by thephoenix » Mon Feb 22, 2010 10:51 pm
Mr. Yutaro's class contains 5boys and 11 girls. If two students are chosen, one at a time, from the class, what is
the probability that a boy and a girl are chosen?
A. 9/48
B. 9/20
C. 11/24
D. 27/48
E. 13/16
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
Legendary Member
Posts: 1275
Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members
Location: Arabian Sea
Thanked: 125 times

by ajith » Mon Feb 22, 2010 11:02 pm
thephoenix wrote:Mr. Yutaro's class contains 5boys and 11 girls. If two students are chosen, one at a time, from the class, what is
the probability that a boy and a girl are chosen?
A. 9/48
B. 9/20
C. 11/24
D. 27/48
E. 13/16
No of ways in which 2 students can be chosen from the group of 16 (11+5) = 16C2 = 16*15/2 = 8*15 =120
No of ways in which 1 girl and 1 boy can be chosen from 11 girls and 5 boys = 11C1*5C1 = 55
[spoiler]
Probability = 55/120 = 11/24[/spoiler]
Always borrow money from a pessimist, he doesn't expect to be paid back.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 140
Joined: Fri Feb 05, 2010 2:43 pm
Thanked: 3 times
GMAT Score:720

by analyst218 » Fri Feb 26, 2010 1:33 pm
Can neone help me understand this more clearly.
I understand why ajith is correct.
However, can't you also say

P(A) = boys
P(B) = girls

P(AandB) = choosing boys and girls?


P(A)*P(BgivenA) = [5/16]*[11/15] = 11/48

I get 11/24 as above when I do P(B)*P(B) = 11/16 * 10/15 = 11/24

Correct me what I'm thinking wrong.....

thanks
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 60
Joined: Wed Jan 07, 2009 1:56 pm
Thanked: 12 times
GMAT Score:750

by arzanr » Fri Feb 26, 2010 8:39 pm
analyst218 wrote:Can neone help me understand this more clearly.
I understand why ajith is correct.
However, can't you also say

P(A) = boys
P(B) = girls

P(AandB) = choosing boys and girls?


P(A)*P(BgivenA) = [5/16]*[11/15] = 11/48

I get 11/24 as above when I do P(B)*P(B) = 11/16 * 10/15 = 11/24

Correct me what I'm thinking wrong.....

thanks
Analyst,

You're thinking is correct but you stopped halfway. The question says that a boy and girl is picked which means that you can either first pick a boy and then a girl or first pick a girl and then a boy. You calculated the probability of picking a boy first and then a girl which is equal to 11/24. Now add the prob of picking the girl first and you get:

11/48 + 11/48 = 22/48 = 11/24
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 140
Joined: Fri Feb 05, 2010 2:43 pm
Thanked: 3 times
GMAT Score:720

by analyst218 » Mon Mar 01, 2010 11:17 am
picking boy and girl= p(boy then girl) + p(girl then boy)
= P(boy)P(girlgivenboy) + p(girl)p(boygivengirl)
= 11/48 + 11/48 = 11/24

makes total sense...
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Thu Jan 09, 2020 6:16 am
thephoenix wrote:Mr. Yutaro's class contains 5boys and 11 girls. If two students are chosen, one at a time, from the class, what is
the probability that a boy and a girl are chosen?
A. 9/48
B. 9/20
C. 11/24
D. 27/48
E. 13/16
P(1 boy and 1 girl chosen) = P(1st selection is boy AND 2nd selection is girl OR 1st selection is girl AND 2nd selection is boy)
= P(1st selection is boy AND 2nd selection is girl) + P(1st selection is girl AND 2nd selection is boy)
= P(1st selection is boy) x P(2nd selection is girl) + P(1st selection is girl) x P(2nd selection is boy)
= 5/16 x 11/15 + 11/16 x 5/15
= 55/240 + 55/240
= 110/240
= 11/24
= C

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1