Question 1088525
If we assume the leading digit can not be zero, then the first 4-digit number is 1000.
The last 4-digit number is 9999.
—
The number of 4-digit numbers is therefore:
9999 - 1000 + 1 = {{{ highlight(9000) }}}

——
Another way to calculate this: 
    1..9  are available for the first digit —> 9 choices
    0..9  are available for the 2nd, 3rd, and 4th digits —> 10 choices for each:  10*10*10 = 1000 choices total
and 9*1000 = <b>9000</b>.