There are 8 rows of chairs in the auditorium. three of the rows are empty. what fraction of the rows are empty?

3 rows out of a total of 8 being empty means a fraction of 3/8 are empty.

This is because the denominator is the total. The total in this case is 8 rows.
The numerator is the number of these rows that are empty. In this case, this is 3 rows.

So the answer is 3/8 of the rows are empty.