1. ## Simple probability question I can't figure out- help please

Hi, I have a probability question I would appreciate help with. Question: if you flip a coin, and continue to flip it, how many times until you would on average get two heads in a row (in immediate succession)?

I understand that if you were to flip the coins in groups of two, one in four of those groups would be two heads (HH, HT, TT, TH). What I’m less sure about is if you’re flipping coins one after the other- at what point, after how many flips, would you on average get two heads (the number including the two heads)?

2. ## Re: Simple probability question I can't figure out- help please

The question isn't clear the way you a phrasing it.

Do you mean what is the expected value of the number of tosses it takes to get two heads in a row?

Yes

4. ## Re: Simple probability question I can't figure out- help please

Originally Posted by Alexander2013
Yes
$E = \sum \limits_{k=0}^\infty~\left(1-\dfrac 1 2 \right)^k\cdot \dfrac 1 4 \cdot (k+2) = \dfrac 3 2$