Please watch and

for which one video is a demonstration of how to calculate factorial, nCr, and nPr on Microsoft Excel.

Then, please decide which counting rule or method applies for any of the following problems:

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?