The mid-value of a class interval is 42. If the class size is 10, then the upper and lower limits of the class are:

(a) 47 and 37

(b) 37 and 47

(c) 37.5 and 47.5

(d) 47.5 and 37.5

Let l and m respectively be the lower and upper limits of the class. Then the mid-value of the class is and the class-size is.

Given that the mid-value of the class is 42 and the class-size is 10. Therefore, we have two equations

Adding the above two equations, we have

Substituting the value of m in the first equation, we have

Hence, the upper and lower limits of the class are 47 and 37 respectively. Thus, the correct choice is (a).