A small town's phone numbers either begin 373 or 377. How many phone numbers are available?

Explanation:

To determine how many phone numbers are available you need to know how many digits the number contains.

I will assume the same number of digits for other similar questions, i.e. 7.

With 7 digits, the numbers that begin with 373 or 377 can be of the form 373 or 377.

Where each X can be any digit 0 - 9. Then, there are 10 different options for each X.

Thus, there are 10×10×10×10 = 10,000 different numbers starting with 373 and other 10,000 different numbers starting with 377.

In total, there are 20,000 numbers available.

the probability is 0