Question

There are 40 students in a class, out of them 15 are boys. The mean of marks obtained by boys is 33 and that for girls is 35. Find out the mean of all students in the class.

Answer 1

$\textbf{Answer}$

$\textbf{We are given following,}$
Total students = 40
Total boys = 15
=> Total girls = 40-15 = 25

Mean of marks of boys = 33
Mean of marks of girls = 35
We have to find the mean of all the students.

$\textbf{What is mean ?}$
$\textbf{Mean}$ can be said as the average of data and we can find the mean of given data by divinding the total sum of all values by the total number of values.

$\textbf{Lets suppose,}$
Sum of the marks obtained of 15 boys = X
=> Mean of marks of all boys = X/15
=> X/15 = 33
=> X = 33×15
=> X = 495

$\textbf{Lets suppose,}$
Sum of the marks obtained by 25 girls = Y
=> Mean of marks of all girls = Y/25
=> Y/25 = 35
=> Y = 35×25
=> Y = 875

So total marks obtained by boys and girls are 495 and 875 respectively.

=> Total marks of all students = 495 + 875

$\textbf{Total marks of all students = 1370}$
&
$\textbf{Total number of students = 40}$

=> Mean of marks of all students = 1370/40

=> $\textbf{Mean of marks of all students = 34.25}$

$\textbf{Hope My Answer Helped}$

$\textbf{Thanks}$

Answer 2

Total number of students = number of boys + number of girls

40 = 15 + number of girls

25 = number of girls

Then,

Mean = { sum of observations }÷{ total number of observations }

By boys,

33 = ( total marks ) ÷ 15

495 = total marks by boys

And

By girls,

35 = ( total marks ) ÷ 25

875 = total marks by girls

Hence, total marks obtained by both = 495 + 875
=> 1370

Total mean = 1370 ÷ 40

Total mean = 34.25

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