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Counting and Probability

  • Thread starter Curtiskr
  • Start date
1
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A seven-digit phone number in the United States consists of a three-digit exchange followed by a four-digit number. How many exchanges are needed to serve a city of 80,000 people?


Combination, Permutation, and arrangement with repetition equations are used in this section.

Part 1 of this question I got right: 8,000,000 people can have phone numbers in one area code if the first digit of the 7 numbers can't be 0 or 1. Part 2 listed above I'm absolutely stumped on though.
 

Answers and Replies

360
21
10,000 numbers per exchange?
 

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