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 April 17th, 2013, 12:50 PM #1 Newbie   Joined: Apr 2013 Posts: 2 Thanks: 0 probability Hi, I've been given a task in the class, it goes like this: A fair coin is tossed n times. Find the probability that the Coin falls on the same side twice... I've been trying to use Binomial distribution but all I've got is an answer with "n", I don't really have any idea where to start... I just need tips of which type of probability needs to be used here...
April 17th, 2013, 02:20 PM   #2
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Re: probability

Quote:
 A fair coin is tossed n times. Find the probability that the Coin falls on the same side twice...
0 on the first toss, 1/2 on the second toss and 1 on the third toss and every toss thereafter.

Do you mean falling on the same side for two consecutive tosses?

 April 18th, 2013, 12:08 PM #3 Newbie   Joined: Apr 2013 Posts: 2 Thanks: 0 Re: probability Yes, the number of times is 'n'.
 April 18th, 2013, 12:24 PM #4 Math Team   Joined: Nov 2010 From: Greece, Thessaloniki Posts: 1,990 Thanks: 133 Math Focus: pre pre pre pre pre pre pre pre pre pre pre pre calculus Re: probability [color=#000000]I don't understand, do you mean $\mathbb{P}\left(\mathbb{X}=2\right)=\binom{n}{2}\l eft(\frac{1}{2}\right)^{2}\left(\frac{1}{2}\right) ^{n-2}=\frac{n!}{2!(n-2)!}\frac{1}{2^n}=\frac{n(n-1)}{2^{n+1}}$?[/color]

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