Given that, total students =100 and number of boys =70 ∴ No. of girls =100−70=30 Average of 100 students =72 ∴ Total marks of 100 students =100×72=7200 Average of 70 boys =75 ∴ Total marks of 70 boys =70×75=5250 ∴ Total marks of 30 girls =7200−5250=1950 ∴ Average marks of 30 girls =