1. How many ways are there to choose 3 people out of 20 people?
2. How many ways are there to choose 3 people to be president, vice-president, and secretary out of 20 people?
3. A baseball team has a 25-man roster. A batting order has nine people. How many different batting orders are there?
4. Given the letters A through G, how many different 4-letter passwords can be made if no letter is used more than once?
