An inlet pipe on a swimming pool can be used to fill the pool in 26 hours. The drain pipe can be used to empty the pool in 30 hours. If the pool is 2/5 filled and then the inlet pipe and drain pipe are opened, how long from that time will it take to fill the pool?

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?