For years, telephone area codes in the united states and canada consisted of a sequence of three digits. the first digit was an integer between 2 and 9, the second digit was either 0 or 1, and the third digit was any integer from 1 to 9. how many area codes starting with a 4 were possible?

The question illustrates permutation and combination.

The total number of area codes starting with 4 is 18.

The selection is as follows:

The total number of selection is:

Hence, 18 area codes starting with 4 are possible.

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The first number had to be 4, so only one option for the first number.

The second number was either 0 or 1, so two options for the second number.

The third number was between 1 and 9, so nine options for the third number.

Multiply each number of options together for total options:

1 x 2 x 9 = 18 different codes could start with 4.

yes.. it's proven to be 36.

using pemdas, (order of operations) you'll see the answer is 24.