Question

The average of 15 boys in an examination is 8. Similarly the average of 25 girls is 6, then find the average mark of that class.

Answer 1

Average mark of that class is 6.75 marks.

Step-by-step explanation:

We are given that the average of 15 boys in an examination is 8. Similarly the average of 25 girls is 6.

As we know that, Mean(Average) formula is given by;

                Mean  =  $\frac{\text{Total sum of all the observations}}{\text{Number of observations}}$

                                    Or

                       $\bar X =\frac{\sum X }{\text{n}}$

where, $\sum X$  =  Total sum of all observations in the data

                n  =  Number of observations

Also,  $\sum X$ = $\bar X \times n$

So, total sum of marks of all 15 boys =  $15 \times 8 =120$

Also, total sum of marks of all 25 girls =  $25 \times 6 =150$

Now, Total sum of marks of all 40 students in class = 120 + 150 = 270

And Total number of students in class = 15 + 25 = 40

Therefore, average mark of that class =  $\frac{270}{40}$

                                                               =  6.75

Hence, the average mark of that class is 6.75 marks.