Convert inclusive class interval 10-19, 20- …

Since the frequency table is in inclusive form we will first convert it into exclusive form by adding h/2 to upper limit and subtracting h/2 to lower limit.
Now we have
         
9.5-19.5                             
19.5-29.5                
29.5-39.5                
39.5-49.5                
49.5-59.5 

Since the frequency table is in inclusive form we will first convert it into exclusive form by adding h/2 to upper limit and subtracting h/2 to lower limit.
Now we have


 

Frequency(f₁)            
9.5-19.5                             
19.5-29.5                
29.5-39.5                
39.5-49.5                
49.5-59.5 

10−19,20−29,30−39,...
Here the class intervals are not continuous. To make them continuous take the mean of upper limit of first class and lower limit of second class.
Mean = (19+20)/2 ​= 19.5, which gives the upper limit of first class and lower limit of second class for the continuous class intervals.