At the start, a jar contains only quarters and coins of lesser value. The average value of these coins is $0.16. Adding a quarter to the jar raises this average value to $0.17. What is the probability that a coin randomly selected from the jar at the start is a quarter?

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?