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