BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

A fair coin

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 537
Joined: Sun Jul 19, 2009 7:15 am
Location: Nagpur , India
Thanked: 41 times
Followed by:1 members

A fair coin

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
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
User avatar
Legendary Member
Posts: 748
Joined: Sun Jan 31, 2010 7:54 am
Thanked: 46 times
Followed by:3 members

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
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
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
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
User avatar
Legendary Member
Posts: 537
Joined: Sun Jul 19, 2009 7:15 am
Location: Nagpur , India
Thanked: 41 times
Followed by:1 members

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
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
Post new topic Post Reply
• Page 1 of 1