Let us find the mean of the obtaining marks of 60 students from the table given below.

Observe, here the class intervals are unequal but continuous. So, in order to find mean we need to simply find midpoints of the class intervals and further find f_ix_i.

We can solve this using three methods,

- Direct method

- Assumed-mean method

- Step Deviation method

We shall calculate the mean using direct method.

So, we have

∑f_ix_i = 748

∑f_i = 64

From direct method, mean is given by

Using the above values,

⇒ Mean = 11.69

Thus, mean is 11.69.