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

  1. 35
  2. 25
  3. 30
  4. 20
Anurag Mishra Professor Asked on 29th December 2015 in Maths.
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1 Answer(s)

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 . 

Monis Rasool Professor Answered on 29th December 2015.
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