Question

(i) Find the class mark of the class 90-120.
(ii) In a frequency distribution, the mid-value of the class is 10 and width of the class is 6. Find the lower limit of the class.
(iii) The width of each of five continuous classes in a frequency distribution is 5 and lower class limit of the lowest class is 10. What is the upper class limit of the highest class?
(iv) The class marks of a frequency distribution are 15, 20, 25, .... Find the class corresponding to the class mark 20.
(v) In the class intervals 10-20, 20-30, find the class in which 20 is included.

Answer 1

(i) class mark =upper limit+lower limit/2=120+90/2=105

(ii) mid-value = 10
width = 6
Let the lower limit of the class be x.
upper limit = x + 6



class mark/mid - value =upper limit+lower limit/2

x+ (x+6 )/2=10

⇒ x = 7
(iii) width = 5
lower class limit of lowest class = 10
The classes will be 10-15, 15-20, 20-25, 25-30, 30-35.
Upper class limit of the highest class = 35.
(iv) Class marks = 15, 20, 25, ...class size = 20 - 15 = 5
Let lower limit of class be x.
x+ (x+5 )/2=20
⇒ x = 17. 5
Thus, the class is 17.5-22.5.
(v) 20 will be included in the class interval 20-30.