You can't be sure, because you haven't specified how many nines are missing.
If 1/9 is short, then18× (1-1/9) =16 people.
, less than 2/9, that is 14 people.
Less than 4/9 is 10 people.
Less than 5/9 is 8 people.
Less than 7/9 is 4 people.
Less than 8/9 are two people.