# How many seven-digit phone numbers can be formed if the first digit cannot be 0 and repetition of digits is not permitted?

##### 1 Answer

Jan 28, 2016

Take it **step-by-step** ...

#### Explanation:

There are 9 ways to pick the first digit [1-9]

Next, there are 9 ways to pick the second digit [0 plus the remaining 8 from the first digit]

The 3rd digit is chosen from the remaining 8 numbers.

The 4th digit is chosen from the remaining 7 numbers.

The 5th digit is chosen from the remaining 6 numbers.

The 6th digit is chosen from the remaining 5 numbers.

The 7th digit is chosen from the remaining 4 numbers.

So, in summary, there are ...

hope that helped