Question

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

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

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

Answer 1

The correct option is C

83.8

We know that,
Average or the mean value of a given number of observations is the sum of all observations divided by the number of observations.
$\Rightarrow \text{Mean}=\frac{\sum x_i{f}_i}{\sum f_i}$

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

$\text{Mean}$
$=\frac{\sum x_i{f}_i}{\sum f_i}$
$=\frac{1676}{20}$
$=83.8$

Thus, mean of the marks obtained by 20 students in a classroom is 83.8.