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 →

A fair coin

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 537
Joined: Sun Jul 19, 2009 7:15 amFollowed by: 1 member
Location: Nagpur , India
Thanked: 41 times
by rockeyb » Wed Apr 07, 2010 5:24 am
Susana flipped a fair coin N times . What fraction of the flips came up heads ?

(1) N= 24.

(2) The number of flips that came up tails was 3/8(N).
"Know thyself" and "Nothing in excess"
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Data Sufficiency |
Junior | Next Rank: 30 Posts
Posts: 12
Joined: Fri Mar 26, 2010 11:57 am

by [email protected] » Wed Apr 07, 2010 7:32 am
(1) N = 24 does not give what fraction of the flips came up heads, insufficient
(2)Tails =3/N and since no other possibility is left except head or tail in a coin flip, heads=1-tail probability=N-3/8N=5/8N
this is sufficient

B is the answer
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 748
Joined: Sun Jan 31, 2010 7:54 amFollowed by: 3 members
Thanked: 46 times

by outreach » Wed Apr 07, 2010 11:17 am
B. the approach is same as given by @hishamby
rockeyb wrote:Susana flipped a fair coin N times . What fraction of the flips came up heads ?

(1) N= 24.

(2) The number of flips that came up tails was 3/8(N).
-------------------------------------
--------------------------------------
General blog
https://amarnaik.wordpress.com
MBA blog
https://amarrnaik.blocked/
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 148
Joined: Tue Jun 09, 2009 11:06 pm
Thanked: 7 times

by pops » Wed Apr 07, 2010 10:29 pm
One very Important thing to note here is a fair coin has equal probability to show heads and tails...
Hence, the probablity of head = probability of tail...
BUT
this should not be used to solve the problem of sequence.. NOTE that the fraction of time coin tossed head converges to 1/2 as number of coin tosses tends to infinity..

this may sound confusing, but should be taken care of !
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 114
Joined: Mon Sep 22, 2008 3:51 am
Thanked: 8 times
GMAT Score:680

by Fiver » Thu Apr 08, 2010 12:13 am
pops wrote:One very Important thing to note here is a fair coin has equal probability to show heads and tails...
Hence, the probablity of head = probability of tail...
BUT
this should not be used to solve the problem of sequence.. NOTE that the fraction of time coin tossed head converges to 1/2 as number of coin tosses tends to infinity..

this may sound confusing, but should be taken care of !
Valid point made.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 1
Joined: Thu Apr 08, 2010 5:38 am

by khamxa » Fri Apr 09, 2010 8:16 am
[email protected] wrote:(1) N = 24 does not give what fraction of the flips came up heads, insufficient
(2)Tails =3/N and since no other possibility is left except head or tail in a coin flip, heads=1-tail probability=N-3/8N=5/8N
this is sufficient

B is the answer
What is 'N' it self in 5/8? dont you think we dont know 'N' individually in statement2, but combining we will know 'N'

Please correct me
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 537
Joined: Sun Jul 19, 2009 7:15 amFollowed by: 1 member
Location: Nagpur , India
Thanked: 41 times

by rockeyb » Fri Apr 09, 2010 8:23 am
@khamxa ,

I would say read the question once again . Do we really need to know what N is ?
"Know thyself" and "Nothing in excess"
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 12
Joined: Fri Mar 26, 2010 11:57 am

by [email protected] » Fri Apr 09, 2010 8:27 am
Ok, the question clearly asks, Susana flipped a fair coin N times . What fraction of the flips came up heads
we need the fraction of N
so without its actual value, statement (2) is sufficient to answer the question but statement (1) alone does not
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1