If you mean only using nines then 99.
9 and 99
99 + 9 = 108
99. 9 divided by 9=1
90
The largest single digit in our numerical system is 9. Once you write 10, you have two digits.
The largest digit is 9.
For this type of "the largest number which..." questions, you need to advance from left to right, using the largest possible digit in each case. For the first two digits, that would be 9, for the third digit (the right-most digit), the largest digit which will make this possible is an 8.
9
It is 9.
The largest one digit number that has three factors is 9. Its factors are 1, 3, and 9.
300
The largest 5 digit number is 99999. If this is divided by 11 it leaves a remainder of 9. Therefore the largest 5 digit number divisible by 11 is 99999 - 9 = 99990.