In a certain class, percentage of students who increased their average grade during spring term compared to that of the fall term was recorded between 6.9% and 7.1%. What could be the least possible number of students in that class?

No, you have to consider that if 1 student in 14/15 cannot represent a percentage between .69 and .71, how could 2 students do the job? You have to have an integer number of students.

2/18 = 1/14 = 7.14%

2/29 = 6.89%

Still out of bounds

What about 3 students?

3/42 = 1/14 = 7.14%

3/43 = 6.97%

3/44 = 6.81%

So, it looks like 43 is the minimum number of students.