Hey.

I was wondering if someone could help me with this...

A fair coin is tossed repeatedly, with successive independent tosses, until two consecutive heads OR two consecutive tails are observed. X is the number of tosses required to achieve this.

Explain why the probability mass function of X is given by:

P(X=n) = (1/2)^(n-1) where n=2,3,4,....

Thank you to all x