In the numbers from 1 to 100, the digit '9' appears 20 times. It appears once in each of the numbers 9, 19, 29, 39, 49, 59, 69, 79, 89, and 90 through 99, as well as twice in the number 99 itself.
Eleven.
20
11
11 with 1 remaining 100 - 1 = 99 = 9 x 11
99 plus 9/9 = 100
(9*9)+(9+9)+(9/9) = 100
5
Nine of them
You can achieve a total of 100 using four 9s with the following equation: ( (99 + \frac{9}{9}) = 100 ). Here, 99 is formed by placing two 9s together, and the fraction ( \frac{9}{9} ) equals 1, which brings the total to 100.
79
One way: 99 + 9/9 = 100
9^2+9+9 +9/9 81+9+9+1=100