An office supply company conducted a survey before marketing a

new paper shredder designed for home use. In the survey, 80% of the people who

tried the shredder were satisfied with it. Because of this high satisfaction rate, the

company decided to market the new shredder. Assume that 80% of all people are

satisfied with this shredder. During a certain month, 100 customers bought this

shredder. Find the probability that of these 100 customers, the number who are

satisfied is

a) exactly 75,

b) 73 or fewer,

c) 74 to 85.