Question 761033
school have grade  9,10,11,12 
each grade have  3   or 4 homerooms
min student each grade will be 10 and max 20 in each home rooms 
min students    will be 
9th grade  10x3=30
10th       10x3=30
11th       10x3=30
12th        10x3=30    total in schools =120
   similarly for  max students per class will be as follow

9th grade  20x4=80
10th       20x4=80   total students  in school will be 320
11th       20x4=80
12th        20x4=80  
ANSWER 
min students   120
max students   320