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 -

Let the number of boys be x
$$\eqalign{ & {\text{Then,}} \cr & {\text{Number of girls}} \cr & = 120\% {\text{ of }}x = \frac{{6x}}{5} \cr & \therefore x + \frac{{6x}}{5} = 66 \cr & \Rightarrow \frac{{11x}}{5} = 66 \cr & \Rightarrow x = \frac{{66 \times 5}}{{11}} \cr & = 30 \cr & {\text{So, number of boys}} \cr & = 30 \cr & {\text{And, new number of girls}} \cr & = \left( {\frac{{6 \times 30}}{5}} \right) + 4 = 40 \cr & \therefore {\text{Required ratio}} \cr & = 30:40 \cr & = 3:4 \cr} $$