In a class of 90 students 60% are girls and remaining are boys. Average marks of boys are 63 and that girls are 70. What are the average marks of the whole class?

67.2

Number of girls = 90 x \(\frac{3}{5}\) = 54

Number of boys = 90 - 54 = 36

Sum of marks of girls = 54 x 70 = 3780

Sum of marks of boys = 36 x 63 =2268

Total marks = 2268 + 3780 = 6048

Average marks of whole class = \(\frac{d6048}{90}\) = 67.2