Question

How many 7 digit phone numbers are possible if the first digit must be non-zero? write your answer in scientific notation.

Answer 1

If the first number is not allowed to be "0", we will have that the aviable numbers will be:

`1,2,3,4,5,6,7,8,9`

So, we will have 9 posibilites, now:

First, we will have that the biggest number of 7 digits that we will be able to write will be 9 999 999 and the smallest is 1 000 000.

Now, we will have that the total number of aviable values is:

`9999999-1000000=8999999`

Then, the total number of possible is:

`8.999999\cdot10^6`