Compute the mode for the following frequency distribution:

Size of items:	0-4	4-8	8-12	12-16	16-20	20-24	24-28	28-32	32-36	36-40
Frequency:	5	7	9	17	12	10	6	3	1	0

Here, the maximum frequency is 17 and the corresponding class is $12-16$. So, $12-16$ is the modal class.
We have,

$l=12,h=4,f=17,f_1=9$ and $f_2=12$

$\therefore Mode=l+\frac{f-f_1}{2f-f_1-f_2}\times h$
$\Rightarrow Mode=12+\frac{17-9}{34-9-12}\times 4$

$\Rightarrow Mode=12+\frac{8}{13}\times 4=12+\frac{32}{13}=12+2.4=14.4$