When three-digit area codes were introduced in 1947, the first digit had to be a number from 2 to 9 and the middle digit had to be either 1 or 0. How many area codes were possible under this system?
To determine the number of possible area codes under this system, we need to consider the possible values for each digit.
- For the first digit, it can be any number from 2 to 9. Therefore, there are 9 possible choices for the first digit.
- For the middle digit, it can be either 1 or 0. Therefore, there are 2 possible choices for the middle digit.
- For the last digit, it can be any number from 0 to 9. Therefore, there are 10 possible choices for the last digit.
To find the total number of possible area codes, we need to multiply the number of choices for each digit together:
Total number of area codes = Number of choices for the first digit × Number of choices for the middle digit × Number of choices for the last digit
Total number of area codes = 9 × 2 × 10
Total number of area codes = 180