# The number of boys in the class is :

The average marks of 50 students in a class is 72. The average marks of boys and girls in that subject are 70 and 75 respectively. The number of boys in the class is

- 35
- 25
- 30
- 20

**Answer is 30**

**Explanation:-**

The total number of students in a class = 50

Let the number boys in the class be X

Then, the number of girls in the class = 50 – X

The average marks of 50 students = 72

Therefore, the total marks of 50 students = 72 x 50

= 3600

The average of boys = 70

Therefore, total marks of boys = 70 X

The average marks of girls = 75

Therefore, total marks of boys = 75 x (50 – X)

So, 70 X + 72 (50 – X) = 3600

70 X + 75 x 50 – 75 X = 3600

– 5 X = 3600 – 3750

– 5 X = – 150

X = 150/5

X = 30

Then, the number of boys in the class is 30.

Hence, the correct answer is option (3) 30 .