two coins are simultaneously tossed until one of them comes up a head and the other a tail. the first coin comes up a head with probability p and the second with probability q. all tosses are assumed independent
(a) Find the PMF, the expected value, and the variance of the number of tosses. P(X=k)=(1−p(1−q)−q(1−p))k−1(p(1−q)+q(1−p)), k=1,2...
And the above is clear for me. Now, we would like determine expected value:
