Question

Find the average marks obtained by 20 students in a class.

$$\begin{array}{cc}Marks& Frequency\\ 87& 2\\ 78& 3\\ 53& 1\\ 98& 2\\ 92& 2\\ 97& 1\\ 81& 2\\ 65& 2\\ 98& 3\\ 76& 2\end{array}$$

• A. 81.8
• B. 82.8
• C. 83.8
• D. 83.4

Answer 1

The correct option is C

83.8

Average or the mean value of a given number of observations is the sum of all observations divided by the number of observations.

$$\begin{array}{ccc}\text{Marks}\left({\text{x}}_{\text{i}}\right)& \text{Frequency}\left({\text{f}}_{\text{i}}\right)& {\text{x}}_{\text{i}}{\text{f}}_{\text{i}}\\ 87& 2& 174\\ 78& 3& 234\\ 53& 1& 53\\ 98& 2& 196\\ 92& 2& 184\\ 97& 1& 97\\ 81& 2& 162\\ 65& 2& 130\\ 98& 3& 294\\ 76& 2& 152\\ \text{TOTAL}& 20& 1676\end{array}$$

Mean = $\frac{\sum {\text{x}}_{\text{i}}{\text{f}}_{\text{i}}}{\sum {\text{f}}_{\text{i}}}$ = $\frac{1676}{20}$ = 83.8