SOLUTION: How many 4 digit number are there when a digit may be repeated any number of times

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Question 1088525: How many 4 digit number are there when a digit may be repeated any number of times
Answer by math_helper(2461) About Me  (Show Source):
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If we assume the leading digit can not be zero, then the first 4-digit number is 1000.
The last 4-digit number is 9999.
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The number of 4-digit numbers is therefore:
9999 - 1000 + 1 = +highlight%289000%29+
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Another way to calculate this:
1..9 are available for the first digit —> 9 choices
0..9 are available for the 2nd, 3rd, and 4th digits —> 10 choices for each: 10*10*10 = 1000 choices total
and 9*1000 = 9000.