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October 6th, 2013, 01:02 PM  #1 
Newbie Joined: Oct 2013 Posts: 3 Thanks: 0  Probability of getting an even number of tails for x throws?
Need help with the formula to calculate the probability for getting an even amount of tails after (0,1,2,...,491) coin flips. would be very thankfull for some help 
October 6th, 2013, 03:09 PM  #2 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,935 Thanks: 1129 Math Focus: Elementary mathematics and beyond  Re: Probability of getting an even number of tails for x thr
If zero is considered even, the probability of getting an even number of tails on zero coin tosses is 1 and the probability of getting an even number of tails on every other number of tosses is 1/2.

October 6th, 2013, 03:17 PM  #3 
Newbie Joined: Oct 2013 Posts: 3 Thanks: 0  Re: Probability of getting an even number of tails for x thr
well i know the probabilityis 1/2 but i think i need to do an binomial of it because i need to figure out the probability of getting a even number of tails in say 491 coin flips

October 6th, 2013, 03:19 PM  #4 
Newbie Joined: Oct 2013 Posts: 3 Thanks: 0  Re: Probability of getting an even number of tails for x thr
only well motivated answers are accepted

October 6th, 2013, 04:06 PM  #5 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,935 Thanks: 1129 Math Focus: Elementary mathematics and beyond  Re: Probability of getting an even number of tails for x thr
There are 2^n possible outcomes, 2^(n  1) of which have an even number of tails. 2^(n  1)/2^n = 1/2.

October 6th, 2013, 04:56 PM  #6 
Global Moderator Joined: May 2007 Posts: 6,762 Thanks: 697  Re: Probability of getting an even number of tails for x thr
You could use mathematical induction on the number of tosses if you want a formal proof.

October 6th, 2013, 05:23 PM  #7  
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,417 Thanks: 1025  Re: Probability of getting an even number of tails for x thr Quote:
 

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