Calculate the additional cash needed for the six months. When there is a cash shortfall (the shortfall/surplus cash calculation is less than zero), additional cash must be obtained from a loan to cover all of the monthly expenses. Therefore, additional cash needed is equal to any cash shortfall. It is zero if there is a cash surplus. The additional cash needed should be a positive number even though a shortfall will be a negative number in the model

Assume that there is a 4% 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 three independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?