Four friends are out for a walk at night and come to an old bridge. it isn’t safe to cross the bridge without a flashlight, and only two people can cross at a time. they only have one flashlight. if the same person carries the flashlight the entire time, what is the minimum number of times that person will have to cross the bridge in order for the entire group to get to the other side?

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.