Question

Find the mean of the marks obtained by 20 students in a classroom.

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

• 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. So, try to obtain the total marks obtained by 20 students in the classroom.

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

Mean = $\frac{\sum x_i{f}_i}{\sum f_i}$ = $\frac{1676}{20}$ = 83.8 i.e. sum total of the marks obtained by 20 students divided by the total number of students.