posted by Anonymous .
Three fair quarters are tossed, and a tail appears on at least one of them. What is the probability that at least one head appears? Express your answer as a common fraction.
For the other two, the probablilty of two tails is 1/2*1/2=1/4
Therefore, pr(at least one head)=1-1/4=3/4
There are a total of eight possible outcomes for three coins: HHH, HHT, HTH, THH, TTH, THT! HTT, TTT. Out of these eight outcomes, seven of these show at least one tail (all except HHH). After counting, we find that six of these seven outcomes have at least one head, so the probability is—6/7.