Question 4

# Numbers of boys and girls are 'x' and 'y' respectively ; average ages of a girl and a boy are 'a' years and 'b' years respectively. The average age (in years) of all boys and girls.

Solution

Number of boys = $$x$$

Average age of boys = $$b$$

=> Total age of boys = $$bx$$

Similarly, total age of girls = $$ay$$

$$\therefore$$ Average age of all boys and girls = Total age of boys and girls / Number of boys and girls

= $$\frac{bx+ay}{x+y}$$

=> Ans - (B)