1. Suppose that 10% of all competitive swimmers use steroids. A test for steroid use will correctly identify 96% of those who use steroids as drug users. The same test will incorrectly flag 10% who do not use steroids as drug users (false positive result).

What is the probability that a swimmer really uses steroids if the test indicates that he/she uses steroids?

2. If a die is rolled 5 times, what is the probability that the number "4" appears exactly twice?