Question

How many different 7-digit telephone numbers are possible if the first digit cannot be 0, but the last two digits must be 0?

Answer 1

The first digit can only range from 1-9, resulting in 9 possible options. The next four digits can range from 0-9, resulting in 10 options for each. Since the last two digits remain the same, they do not affect the sample size. Using the fundamental counting principle, we can find the amount of telephone numbers possible in the following equation.
$9 \times 10 \times 10 \times 10 \times 10 \times 1 \times 1 \\ 90000$