Answer all questions with explanation

McDonald fast food conducted a taste survey before marketing a new fruit salad. The results of the survey showed that 80% of the people who tried this salad liked it. Encouraged by this result, McDonald decided to market the new salad. Assume that 73% of all people like this salad. On a certain day, twenty customers bought it for the first time.

a) What is the probability at most 4 customers like this new fruit salad?

b) What is the mean and standard deviation of this probability distribution?