SSC CHSL 20 Dec 2015 Shift 1 Paper

Given average marks of 50 students in a class is 72. Then total marks is given by,
T = 50 x 72 = 3600
If total number of boys are B then total girls will be (50-B).
And also average marks of boys is 70 and that of girls is 75. Then equation can be written as,
T = 70(B) + 75(50 - B) ⇒ 3600 = 70B - 75B + 3750
⇒ 5B = 150 B = 30
Hence, option D is the correct answer.