# Mode for unequal class length

##### Member
How to find mode for grouped frequency distribution with unequal class length? I have to find the mode for the following problem:

Marks No of students

0-20 32
20-50 45
50-70 15
70-100 8

For equal class length, we use the formula

$$\displaystyle Mode= l+\frac{f_0-f_{-1}}{2f_0-f_{-1}-f_{+1}}$$

But how to proceed for the above example?