Every year group in Jane's school has more than 110 pupils but fewer than 130. Jane's entire year had a test with two questions and everyone in the year answered at least one of the questions correctly. Each of the questions was correctly solved by 68% of the pupils. How many pupils answered both questions correctly?

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?