Question

how to change class intervals continuous if not

Answer 1

the solution we get by subtracting the lower limit of 2nd class interval and upper limit of 1st class should added to upper limits of all classes and subtracted from lower limit of all classes
for example
17-19
20-22
23-25
26-28
is given we make it continuous in this way 20-19/2=0.5
therefore the classes are 16.5-19.5
19.5-22.5
22.5-25.5
25.5-28.5

hope it helps...

Answer 2

 for example let  the classes are 
20-29
30-39
40-49
u can change it as 
19.5 - 29.5 here lower limits are subtracted 0.5 upper limits added 0.5 
29.5 - 39.5
39.5 - 49.5