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A typical Social Security number is 555-47-5593. How many Social Security numbers are possible
if the first three digits cannot be 1?
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If all nine-digit Security numbers be allowed from 000-00-0000 till 999-99-9999,
the amount of such numbers would be 1,000,000,000 (one billion).
But, according to the problem, Security numbers from 111-00-0000 to 111-99-9999 are prohibited.
The amount of the prohibited numbers is 1,000,000 (one million).
So, the ANSWER to the problem's question is this difference
1,000,000,000 - 1,000,000 = 999,000,000.
Solved.