A coin is tossed twice. If the outcome is at most one tail, what is the probability that both head and tail have appeared?
A coin has 2 sides and its sample space S={H,T}
The total number of outcomes = 2.
A coin is tossed twice.
Let P(A) be the probability of getting at most 1 tail.
The sample space of A = {(H,H),(H,T),(T,H)}
Let P(B) be the probability of getting a head.
The sample space of B = {H}
The probability of getting at most one tail and a head
Tip – By conditional probability, 
where 
is the probability of occurrence of the event A given that B has already occurred.
The probability that both head and tail have appeared:
1