Andrea has just purchased a five-digit combination lock. It allows her to set up her own combination. She can use the numbers 0 through 9 for her combination, and she must use five digits.

1. How many five-digit combinations can she make so that no digit is repeated?

   Hint (a):

   There are no repeats, but order does matter.

   Answer (a):

   ₁₀P₅ = 30,240

2. How many five-digit combinations are possible if she can repeat the digits, but cannot use the same digit twice in a row?

   Hint (b):

   Now she has ten choices for each digit.