2-15 A silver dollar is flipped twice. Calculate the probability of each of the following occurring: a. a head on the first flip b. a tail on the second flip given that the first toss was a head c. two tails d. a tail on the first and a head on the second e. a tail on the first and a head on the second or a head on the first and a tail on the second f. at least one head on the two flips