Need math help: How many international direct dialing number?

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How many international direct-dialing numbers are possible if each number consists of a four-digit area code (the first digit of which must be nonzero) and an eight-digit telephone number (the first digit must be nonzero)?
A.
B.
C.
D.
E.
Nov 15th, 2015

Thank you for the opportunity to help you with your question!

We have 4 + 8 = 12 number of events occurring simultaneously.

Where these 12 events represent the digit values.

1st digit has only 9 possible values.

5th digit has only 9 possible values.

The rest of the 10 digits have 10 possible values.

We multiply their individual possible outcomes and get:

(9^2 )*(10^10) = 810,000,000,000

Answer choice C.) 810,000,000,000

Please let me know if you need any clarification. I'm always happy to answer your questions.
Nov 15th, 2015

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Nov 15th, 2015
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Nov 15th, 2015
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