Two variables are said to interact when . a. the two variables are differentially affected by a third variable b. both variables produce a change in the subjects' scores c. both variables are equally influenced by a third factor d. the effect of one independent variable depends on the levels of the second variable

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?