Statistics : Standard Deviation of a Frequency Distribution

The first 2 columns are given to you. ( x and f)

The table below shows the distribution of marks in an examination. Calculate the S.D of this set of data.

 $\overline{x}\ =\frac{\in xf}{\in f}=\frac{300}{60}=5$  
 $S.D.\ =\sqrt{\frac{\in\left(x-\overline{x}\right)^2f}{\in f}\ }=\sqrt{\frac{292}{60}}=2.21$  
The data is relatively normal.

The frequency table below shows the distribution of heights of 100 students at a school. Find the S.D of this data.

 $\overline{x}\ =\frac{\in fx}{\in f}=\frac{15870}{100}=158.7$