Choose 5 digits from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 without replacement to form a five-digit number. How many different ways to form an odd number are there?

A five-digit number does not start with 0.

Consider five people: A, B, C, D, and E. How many different ways can the five people sit in a row of five chairs at a movie theatre if A and B want to sit side by side?

Consider five people: A, B, C, D, and E. How many different ways can five people sit in a row of five chairs at a movie theatre if A and B refuse to sit side by side? It means that there must be at least one person between A and B.

Choose 4 shoes from 6 pairs of shoes such that there is no matching pair of shoes. How many choices are there?