Question 1162160
<br>
The answer from the answer key -- 7*9*9*10*10*10*10 -- makes no sense.  There is no way to solve the problem simply by finding the numbers of choices for each of the 7 digits.<br>
There are no restrictions on the last four digits; there are 10 choices for each of those.<br>
For the first three digits, all the 3-digit numbers 200 to 999 except for 411 and 911 are allowed.  That's 800-2 = 798 possibilities for the first three digits.<br>
So the number of 7 digit phone numbers is 798*10^4 = 7,980,000.<br>
Your answer is correct; the answer key is wrong.<br>