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Question
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:
Options
47 and 37
37 and 47
37.5 and 47.5
47.5 and 37.5
Solution
Let l and m respectively be the lower and upper limits of the class. Then the mid-value of the class is`(l+m)/2` and the class-size is (l-m) .
Given that the mid-value of the class is 42 and the class-size is 10. Therefore, we have two equations
`(l+m)/2 =42`
`⇒ l +m = 84,`
m- l =10
Adding the above two equations, we have
`(l+m) +(m-l)= 84+10`
`⇒l+m+m-l=94`
`⇒2m = 94`
`⇒ m = 47`
Substituting the value of m in the first equation, we have
`l+47= 84`
`⇒l= 84-47`
`⇒ l = 37`
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