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 of girls is 35 find out the mean of all students in the class.

Answer 1

total students = 40
no. of boys = 15
no. of girls = 40-15 = 25
now,
mean marks by boys= 33
sum of all marks by boys be X1
therefore,
X1/15 = 33
X1 = 33×15 = 495

let sum of marks by girls be X2.
mean marks by girls = 35.
therefore,
X2/25 = 35
X2 = 35×25 = 875

now total sum of marks by all students = X1+X2
= 495+875
= 1370
now. total mean marks = total sum / total students
= 1370/40 =34.25.....ANS.

Answer 2

Heya,

Given:-
Total no.of students = 40
Total no.of boys = 15
Total no. of girls = 40-15 = 25
Mean marks of boys = 33
Mean mark of girls = 35

To find:-
Mean of all students

Solution:-
Let's assume,

Sum of marks of boys = x
Sum of marks of girls = y

Therefore,
x/Total boys = 33 (mean)
x/15 = 33
× = 33 × 15
x = 495

y/Total girls = 35 (mean)
y/25 = 35
y = 25 × 35
y = 875

=> Total marks by all = x + y
=> Total marks by all = 495 + 875
=> Total marks by all = 1370

Therefore,
Mean of all students = Total mark/Total students
Mean of all students = 1370/40
Mean of all students = 137/4
Mean of all students = 34.25

Hope my answer helps you :)

Regards,
Shobana