Answer:
Step-by-step explanation:
Student : teacher = 5 : 2
Number of students = 5x
Number of teachers = 2x
Last year:
Last year Total  = 56
5x+ Â 2x = 56
    7x = 56
    x = 56/7
x = 8
Number of students = 5*8 = 40
Number of teachers = 2*8 = 16
This year:Total = 70
5x + 2x = 70
    7x = 70
    x = 70/7
x = 10
Number of students = 5*10 = 50
Number of teachers = 2*10 = 20