Eleven.
Five 9s:(99 x 9 + 9) / 9 = 100
11
11 with 1 remaining 100 - 1 = 99 = 9 x 11
Of whole numbers only, it's 449. Of all numbers including decimals, it's 449.99999... with the 9s never ending.
99 plus 9/9 = 100
(9*9)+(9+9)+(9/9) = 100
Yes, there are an infinite number of posibilities. Staying only with positive odd numbers, if duplicates are allowed, then five 9s and five 11s make 100. If duplicates are disallowed, then 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 = 100
5
Nine of them
There are exactly 20 Nines. 9,19,29,39,49,59,69,79,89,90,91,92,93,94,95,96,97,98 which totals 18 and the last number 99 has 2 nines and therefore 20 nines in total.
79