Matthew flips 2 coins, what is the probability that he will get

Question

a.  only one tail.                                                                      b.  two heads.

Answer 1

one tail can happen two ways, either TH or HT

Pr(1 Tail) = Pr(TH) + Pr(HT) = 1/2 x 1/2 + 1/2 x 1/2 = 1/4 + 1/4 = 1/2

Pr(of just one tail) = 1/2 which is the same as the probability of just one head

Pr(2 heads) = 1/2 x 1/2 = 1/4

Pr(2 tails) = 1/2 x 1/2 = 1/4

those are all three possibilities. Their probabilities sum to 1.

1/2 +1/4 +1/4 = 1