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The Brainliest Answer!
2015-03-10T13:27:54+05:30
Given, CM= 15,20,25,30,35.....
Since the CM are of equal width, then class size= 20-15=5
Using the formula:
a+(h/2) and a-(h/2), Where a= CM and h=class size
Substituting,
20+(5/2)=20+2.5=22.5
20-(5/2)=20-2.5=17.5
Therefore, class (CM=20) is 22.5-17.5
Again, 
25+(5/2)=25+2.5=27.5
and 25-(5/2)=25-2.5=22.5
Therefore, Class= 22.5-27.5
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2015-03-10T13:56:28+05:30
Class corresponding to class mark 20 and 25.
   We can directly see that with the class corresponding rule (n+h/2 and n-h/2) the class corresponding to class mark 20 and 25 = 22.5-27.5
  I think u got the rule.
so, plzzzzzzzzzzz  mark thanks for my answer.
      
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