My Math Forum Probability question

 January 27th, 2011, 04:03 PM #1 Newbie   Joined: Feb 2009 Posts: 21 Thanks: 0 Probability question Question : How many times should a coin be tossed so that the probability of at least one head is >= 99% Attempt, straight from the definition : P(N = n) = (1-p)^(n-1) * p, where p is the probability of success 0.99 = (1-1/2)^n * 1/2 0.99 = (1/2)^n n = 0.0145 What am I doing wrong?
January 27th, 2011, 04:31 PM   #2
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Re: Probability question

Quote:
 Originally Posted by tnutty What am I doing wrong?
You're calculating the probability of flipping n coins, all but the last being tails and the last being heads. It's an entirely different problem.

You should set the odds of getting all tails to 1% and solve.

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