Question 1206217
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I found this online:<i>
Using 0 or 1 as the first digit of an area code or central office 
code is invalid, as is a 9 as the middle digit of an area code; 
these are trunk prefixes or reserved for North American Numbering 
Plan expansion.</i>

Perhaps you should mention this to your teacher.

The trick for finding how many integers there are from A to B, inclusive,
is to subtract 1 less than the smallest from both the smallest and the largest:

You got the first correct, if you ignore the above.

100-0000 to 999-9999, or without the hyphen:
1000000 through 9999999

Subtract 1 less than the smallest, or 999999 from each

That's the integers 1 through 9000000.  You got that.

Doesn't the (b) part mean that you just put a 1 before each of those in the
(a) part?  Wouldn't it just be the same number?

Edwin</pre>