Which property of a rigid transformation is exclusive to rotations?

Ineed i been stuck on this question since yesterday

Ming says that 0.24 > 1/4 because 0.24= 2/4. which best explains mings error

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?