Find the mean of each of the following frequency distributions :

Let the assumed mean be A = 50 and h = 10.

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

Now, we have $N=\sum f_{i}=40, \sum f_{i} u_{j}=-2, h=10$ and $A=50$.

Putting the values in the above formula, we have

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

$=50+10\left(\frac{1}{40} \times(-2)\right)$

$=50-\frac{20}{40}$

$=50-0.5$

$=49.5$

Hence, the mean is 49.5.