The probability that the coin when tossed turns up heads is 1/2. This means that when the coin is tossed, the probability of tails is 1 – 1/2 = 1/2. When the coin is tossed twice, the probability of getting only tails is 1/2* 1/2 = 1/4. The probability of getting at least one heads is 1 – 1/4 = 3/4.