With no digit rejected, 999999999 With no digit repeated, 987654321
94205 if digits are not to be repeated and 99999 if digits can be repeated
The greatest 3-digit number is 999. 9+9+9 = 27 The sum of the greatest 3-digit number is 27.
The number 9 is the greatest one-digit number.
Since the greatest digit is 9 and the greatest 2-digit number is 99, the product of them is 891.
987654321 is the highest nine-digit number with no repeated digits.
For this kind of question, start from the left, and use the greatest possible digit for each position. Thus, in the first position you would have a 9, in the second an 8, etc.
Since the greatest 1-digit number is 9, the answer is 9 x 9 = 81.
It is 999999998.