SSC CPO SI and ASI Model Paper 10

(2) Let the number of males in thesociety be x and the number of femalesbe y.
Sum of the ages of males in thesociety = 21x yrs.
Sum of the ages of females in thesociety = 18y yrs.
Average age of people in the society= 20
$\therefore \frac{21\mathit{x}+18\mathit{y}}{\mathit{x}+\mathit{y}}=20$
⇒21x + 18y = 20(x + y)
⇒21x + 18y = 20x + 20y
⇒21x – 20x = 20y – 18y
⇒x = 2y
⇒x/y=2/1
∴ Ratio of the number of males tothe number of females is 2 : 1.