SOLUTION: How many 4 number PIN numbers can be formed using the digits 0-9 if repetition is allowed? If repetition is NOT allowed?

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Question 312488: How many 4 number PIN numbers can be formed using the digits 0-9 if repetition is allowed? If repetition is NOT allowed?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
With repetition,
N=10%2A10%2A10%2A10=10000
Without repetition,
N=10%21%2F%2810-4%29%21=10%21%2F6%21=10%2A9%2A8%2A7=5040