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A fair coin

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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).
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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
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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).
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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 !
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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.
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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
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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 ?
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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
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