A fair die is tossed seven times. Let us assume that success occurs if a 5 or 6 appear. Let \(n=7, p=P\{5,6\}=\frac{1}{3}\), and \(q=1-p=\frac{2}{3}\).

(a) What is the probability that a 5 or a 6 occurs exactly three times (i.e., \(k=3\) )?

(b) What is the probability that a 5 or a 6 occurs at least once?