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10-21.

Andrea has just purchased a five-digit combination lock. It allows her to set up her own combination. She can use the numbers through for her combination, and she must use five digits. For help with this problem, refer to the Math Notes box in this lesson. Homework Help ✎

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

    There are no repeats, but order does matter.

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

    Now she has ten choices for each digit.