A boat travels at a speed of 20 miles per hour in still water. It travels 48 miles upstream, and then returns to the starting point in a total of five hours. The speed of the current is ? miles per hour

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?