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 August 14th, 2018, 09:43 AM #1 Newbie   Joined: Aug 2018 From: United States Posts: 3 Thanks: 0 Probability Interview Question Toss a coin until the nth Head turns up. Let Y = number of required tosses, calculate P(Y is even), set p=P(H), q=P(T). Last edited by skipjack; August 14th, 2018 at 11:05 AM.
 August 14th, 2018, 01:53 PM #2 Global Moderator   Joined: May 2007 Posts: 6,807 Thanks: 717 $P(Y=n)=q^{n-1}p$. Therefore $P(Y\ is\ even)=p\sum_{k=1}^{\infty}q^{2k-1}=\frac{pq}{1-q^2}=\frac{q}{1+q}$ Thanks from AAA Last edited by mathman; August 15th, 2018 at 04:22 PM. Reason: add material

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