Question

how to make class intervals continuous
please fast

Answer 1

subtract 0.5 from the lower limit and add 0.5 to the upper limit
eg: 31-45
      46-50
i.e. 31-0.5  -    45+0.5 &
      46-0.5  -    50+0.5
which is 
    30.5-45.5
     45.5-50.5

Answer 2

In order to make class intervals continuous, you are supposed to subtract 0.5 from the lower limit and add 0.5 in the upper limit.