Find the mean of each of the following frequency distributions :

Let the assumed mean be A = 15 and h = 6.

We know that mean, $\bar{X}=A+h\left(\frac{1}{N} \sum f_{i} u_{i}\right)$

Now, we have $N=\sum f_{i}=40, \sum f_{i} u_{i}=3, h=6$ and $A=15$.

Putting the values in the above formula, we get

$\bar{X}=A+h\left(\frac{1}{N} \sum f_{i} u_{i}\right)$

$=15+6\left(\frac{1}{40} \times(3)\right)$

$=15+\frac{18}{40}$

$=15+0.45$

$=15.45$

Hence, the mean is 15.45.