If a:b= 4:5, a:c= 1:2 then b:c=?

If x : y = 3 : 1, then x³– y³ : x³ + y³ =?

If A: B: C = 3:4:5 and B= x% of (A+C), then x is equal to?

In a class the number of girls is 20% more than that of the boys. The strength of the class is 66. If 4 more girls are admitted to the class, the ratio of the number of boys to that of the girls is