The average marks of a class of 30 students is 50 and that of another class of 50 students is 60. Find the average marks of all the students? Choose the correct choice from the following:  A) 56.25  B) 52.9  C) 52.1  D) 52.3  E) 42.5

Rationale: "sum of the marks for the class of 30 students = 30 * 50 = 1500 sum of the marks for the class of 50 students = 50 * 60 = 3000 sum of the marks for the class of 80 students = 1500 + 3000 = 4500 average marks of all the students = 4500 / 80 = 56.25 answer : a"
Answer: A