What real number is 7/8

If 20% of a number is 35, what is 50% of that number?

The sum of the squares of two numbers is 8 . the product of the two numbers is 4. find the numbers.

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?