Statistics and Probability

Consider the following distribution :

Marks  obtained              Number  of  students

More than or equal to 0       63

More than or equal to 10     58

More than or equal to 20     55

More than or equal to 30     51

More than or equal to 40     48

More than or equal to 50      42

the frequency of the class 30-40 is

(A) 3 (B) 4 (C) 48 (D) 51