Athief steals an atm card and must randomly guess the correct five-digit pin code from a 4-key keypad. repetition of digits is allowed. what is the probability of a correct guess on the first try?

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?