Convert the following frequency distribution to exclusive form :

Class Interval	Frequency
30 – 34	7
35 – 39	9
40 – 44	13
45 – 49	6
50 – 54	3
55 – 59	10

Use this table to find :

(i) The true class-limits of the fourth class-interval.

(ii) The class-boundaries of the fifth class-interval.

(iii) The class-mark of the third class-interval.

(iv) The class-size of the sixth class-interval.

Adjustment factor

= $\dfrac{\text{Lower limit of one class - Upper limit of previous class}}{2} = \dfrac{35 - 34}{2} = \dfrac{1}{2}$ = 0.5

Subtract the lower limit of each class by 0.5 and add 0.5 to upper limit of each class.

(i) The true class limits of the fourth class interval is 44.5 - 49.5.

(ii) The class-boundaries of the fifth class interval is 49.5 - 54.5.

(iii) The class-mark of the third class interval

= $\dfrac{39.5 + 44.5}{2}$

= $\dfrac{84}{2}$

= 42.

Hence, the class mark of third class interval = 42.

(iv) Sixth class interval : 54.5 - 59.5

Class size = Upper limit - lower limit

Class size = 59.5 - 54.5 = 5.

Hence, the class size of sixth class interval is 5.