Correct Answer - Option 1 : 7.8
Formula used :
Average = Sum of all values/Number of values
Let the number of girls be 'g'
Let the number of boys be 'b'
Total number of boys and girls = b + g
Total marks of girls in English = 9 × g = 9g
Total marks of boys in English = 8 × b = 8b
Total marks in English 9g + 8b
According to the question
⇒ 8.8 = (9g + 8b)/(b + g)
⇒ b : g = 1 : 4
Number of boys = x and number of girls = 4x
Total number of boys and girls = x + 4x = 5x
Now, total marks in Hindi
Marks of girls in Hindi = 8 × 4x = 32x
Marks of boys in Hindi = 7 × x = 7x
Average of marks in Hindi = (32x + 7x)/5x (total marks = 32x + 7x)
∴ The average marks in Hindi will be 7.8.