An online data base charges $25 an hour during the day and $12.50 an hour at night. if a research company paid $250 for 12 hours of use, which system of equations could be used to determine the number of hours charged at the day rate (d) and at the night rate (n)?

a)
d + n = 12
25d + n = 250
b)
d + n = 12
25d + 12.50n = 250
c)
d − n = 12
25d + 12.50n = 250
d)
d + n = 250
25d − 12.50n = 250

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.