James and sarah went out to lunch the price of lunch for both of them was $20 they tip their server 20% of that amount how much did each person pay if they share the price of lunch at the tip equally

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?