consider the following grouped data:

Class Interval	Number of students
20-25	8
25-30	14
30-35	20
35-40	18
40-45	10
45-50	6

The highest frequency is $20$, so the modal class is:

$30-35$

For grouped data, mode is given by:

$\text{Mode}=l+\frac{f_1-f_0}{2f_1-f_0-f_2}\times h$

Here,

$l=30$

$f_1=20$

$f_0=14$

$f_2=18$

$h=5$

Now,

$\text{Mode}=30+\frac{20-14}{2(20)-14-18}\times 5$

$\text{Mode}=30+\frac{6}{40-32}\times 5$

$\text{Mode}=30+\frac{6}{8}\times 5$

$\text{Mode}=30+3.75$

$\text{Mode}=33.75$