According to a study, the probability that a randomly selected teenager shopped at a mall at least once during a week was 0.65. let x be the number of students in a randomly selected group of 60 that will shop at a mall during the next week. (a) compute the expected value and standard deviation of x. (round your answer to two decimal places.) hint [see example 5.]

Assume that there is a 11% rate of disk drive failure in a year. a. if all your computer data is stored on a hard disk drive with a copy stored on a second hard disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive? b. if copies of all your computer data are stored on four independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?