For each 90 mm of coloured fabric Paul uses to make his curtains, he also uses 10 cm of white fabric. Express the amount of white fabric to coloured fabric as a ratio in its simplest form.

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?