SOLUTION: A campus telephone extension has four digits. If the first digit cannot be 0, how many different extensions exist?

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Question 1001359: A campus telephone extension has four digits. If the first digit cannot be 0, how many different extensions exist?
Answer by ikleyn(52794) About Me  (Show Source):
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There are 9 options for the first digit (1, 2, 3, 4, 5, 6, 7, 8, 9);
10 options for the second digit;
10 for the third, and
10 for the fourth digit.

In total, there are 9*10*10*10 = 9000 options for 4-digit extension.