Hot air balloons generally descend at a rate of 200 to 400 feet per minute. four balloons descend 200 feet per minute for 9 minutes. find the total change in altitude for all 4 balloons.

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?