Suppose a coin is tossed until a head appears. Let p be the probability of a head on any given toss. Define random variable X to be the number of tosses required to obtain a head.

a) State the set of values that X can take on. Is this finite or countably infinite set?

b) What is the PMF (probability mass function) of X? If p = 1/4, what is the probability that X=10?

Can any one help on this question??