Find Out the number of boys in the Class? If

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
Monis Rasool Professor Asked on 23rd December 2015 in Maths.
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  • 1 Answer(s)

    Answer:  (3) 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 . 

    Anurag Mishra Professor Answered on 27th December 2015.
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