Question

The internal telephone numbers in the phone system on a campus consists of 4 digits, with the 1st not equal to 0. How many different numbers can be assigned in this system?

Answer 1

Answer:

This system have 9000 different numbers.

Step-by-step explanation:

We know that the internal telephone numbers in the phone system on a campus consists of 4 digits, with the 1st not equal to 0.

We have total 10 digits.

In the first place we have 9 possibilities, because from the conditions of the task in the first place there cannot be 0.

In second, third and fourth place we have 10 possibilities.

Therefore, we get

$N=9\cdot 10\cdot10 \cdot 10=9000$

This system have 9000 different numbers.