Evaluate the following using identity ( part 2 ) 4. (0.4a + 1/4 b) (0.4a - 1/4b)
5. (x + 1/y) ( x-1/y)
6. (2/3x + 3/11y) (2/3x - 3/11y)

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 69 or fewer.