In a class of 100 students. there are 70 boys whose average marks in a subject are 75. If the average marks of the complete class is 72, then what is the average of the girls?

Solution :

Since, total number of students = 100

and number of boys = 70

\(\therefore\) number of girls = (100 – 70) = 30

Now, the total marks of 100 students = 100*72 = 7200

And total marks of 70 boys = 70*75 = 5250

Total marks of 30 girls = 7250 – 5250

\(\therefore\)  Average marks of 30 girls = \(1950\over 30\) = 65

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