Sally's pet store sells goldfish. The fish they sell, every goldfish needs 4 gallons of water in the tank. Frank's pet store sells goldfish as well. At Frank's every 4 fish need 3 gallons of water. If a customer has a 12 gallon tank, where should they buy the fish from?

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?