Answer
$1,000,000,000$
Work Step by Step
See page 690, The Fundamental Counting Principle:
The number of ways in which a series of successive things can occur is found by multiplying the number of ways in which each thing can occur.
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Ways of choosing the
1st digit ... 10 (any of digits 0 - 9),
2nd digit ... 10,
3rd digit ... 10,
...
9th digit ... 10.
Total: 10$\times$10$\times$...$\times$10$=10^{9}=1,000,000,000$
(This includes the number 000-00-0000. There are no constraints by which we should exclude it, so $1,000,000,000$ remains as the answer)
