Question

if the mid values of the class intervalsa are 12,18,24,30,36,then find the class interval with 18 as mid value.

Answer 1

Given:
Mid values of Class Interval are 12,18,24,30,36

To Find:
Class Interval with 18 as mid value.

solution:

size of Class Interval = Difference between the midvalues of any two consecutive classes= 18-12=6

The class boundaries for different class interval is obtained by adding half of the magnitude of class interval for upper class interval and subtracting half of the magnitude for lower class interval.

So class interval with 18 as mid value:
upper class interval = 18+ 6/2=18+3=21

lower class interval= 18-6/2=18-3=15

Therefore class interval with midvalues 18 is 15-21

Answer 2

Since the class marks are Equally spaced

Class size = 18-12= 6

If 'a' is a class mark & h is size of class interval then lower limit and upper limit of the interval are a- h/2 & a+h/2.

We have h = 6

Lower Limit of first class interval
= 12- 6/2 = 12-3= 9

Upper limit of first class interval
= 12+ 6/2= 12+3= 15

First class interval is 9 - 15

The class intervals are 9-15, 15-21, 21- 27, 27- 33, 33- 39

Mid value of class interval (15-21)= (21+15)/2= 36/2=18

Hence, the class interval with 18 as a mid value= 15 - 21

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Hope this will help you....