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. For help with this problem, refer to the Math Notes box in this lesson.

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):

   $_{10}P_5= 30{,}240$

2. How many five-digit combinations are possible if she can repeat the digits?

   Hint (b):

   Now she has ten choices for each digit.