The average marks of a class of 28 students is 40 and that of another class of 50 students is 60. Find the average marks of all the students?  Choices.
A) 52.2 B) 59.5 C) 52.8 D) 52.5 E) 52.1

Rationale: "sum of the marks for the class of 28 students = 28 * 40 = 1120 sum of the marks for the class of 50 students = 50 * 60 = 3000 sum of the marks for the class of 78 students = 1120 + 3000 = 4120 average marks of all the students = 4120 / 78 = 52.8 answer : c"
Answer: C