Numbers of girls in a class = 20
Numbers of boys in a class = 15
Total numbers of students in a class = 20 + 15 = 35
(a) Ratio of number of girls to number of boys
= 20/15 = 4/3 = 4 : 3
(b) Ratio of numbers of girls to total number of students
= 20/35 = 4/7 = 4 : 7