## Thinking Mathematically (6th Edition)

$1,000,000,000$
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. --------- 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)