SOLUTION: Two-digit numbers are made up from the digits 0, 1, 2, and 3. How many numbers can be made if 0 cannot be the first digit and the repetition of digits is allowed?

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Question 523772: Two-digit numbers are made up from the digits 0, 1, 2, and 3. How many numbers can be made if 0 cannot be the first digit and the repetition of digits is allowed?
Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
When making a two-digit number,

you can choose the first digit any of 3 ways, 1, 2, or 3.

For each of those 3 ways to choose the first digit, there
are 4 ways to choose the second digit, either 0, 1, 2, or 3.

So that's 3×4 or 12 ways in all  Here are all 12 ways:

 1.  10
 2.  11
 3.  12
 4.  13
 5.  20
 6.  21
 7.  22
 8.  23
 9.  30
10.  31
11.  32
12.  33

Edwin