(a) Let the number of boys and girls in the class are m and n respectively, so according to given informations, Total marks of boys =40m and total marks of girls =45n and total marks of boys and girls =42(m+n) ∴40m+45n=42(m+n) ⇒2m=3n⇒
m
3
=
n
2
=λ ∴40m+45n=42(m ⇒2m=3n⇒
m
3
=
n
2
=λ ∴m=3λ and n=2λ So, the percentage of boys in the class is