Concept:Probability is the number of favourable outcomes divided by the total number of possible outcomes.Explanation:When a fair coin is tossed twice, the sample space is S={HH,HT,TH,TT}.So, the total number of possible outcomes is n(S)=4.The event of obtaining at least one head includes HH, HT, and TH.So, the number of favourable outcomes is n(A)=3.Therefore, the probability is P=n(S)n(A)=43=0.75.
