Question

Find the mean, using direct method:

$\begin{array}{cccccc}\text{Class}& 0-10& 10-20& 20-30& 30-40& 40-50\\ \text{Frequency}& 3& 5& 9& 5& 3\end{array}$

Answer 1

$\begin{array}{cccc}\text{Class}& \text{Class Marks}\left(x_i\right)& \text{Frequency}\left(f_i\right)& f_i{x}_i\\ 0-10& 5& 3& 15\\ 10-20& 15& 5& 75\\ 20-30& 25& 9& 225\\ 30-40& 35& 5& 175\\ 40-50& 45& 3& 135\\ & \sum x_i=80& \sum f_i=25& \sum f_i{x}_i=625\end{array}$

$\therefore$ Mean $=\frac{\sum f_i{x}_i}{\sum f_i}=\frac{625}{25}=25$