What is the difference between the greatest 4-digit number and the smallest 2-digit number?
 
                Answer: 
            
        9989
- The  greatest 4-digit number can be formed by placing the greatest digits in the  thousands, hundreds, tens, and ones place, respectively. 
 Thus, 9999 becomes the greatest 4-digit number.
- Similarly, the smallest 2-digit number can be formed by placing the smallest digit in the   tens  and ones place, respectively. 
 But we cannot place 0 in the highest place value as the new number,thus formed, will actually be a 2-digit number.
 Thus, 10 becomes the smallest 2-digit number.
- According to the question, we have to find the difference between the greatest 4-digit number and the smallest 2-digit number.
 So, 9999 - 10 = 9989.
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