A coin is tossed until a head appears or it has been tossed thrice. Given that head doesn't appear on the first toss, the probability that coin tossed thrice is

Step-by-step solution

A coin is tossed until a head appears or it has been tossed thrice. Given that head doesn't appear on the first toss. Total possible cases or sample space = H , T H , T T H , T T T Probability of head = P H = 1 2 Probability of first tail and second head = P T H = 1 2 × 1 2 = 1 4 Probability of first two tails and third head = P T T H = 1 2 × 1 2 × 1 2 = 1 8 Probability of three tails = P T T T = 1 8 Let, A = Head doesn't appear on the first toss P ( A ) = P ( T ) = 1 2 B = Coin tossed thrice