Question

John's age was the square of his son’s age six years ago. After nine years, John's age will be twice his son's age.

(iii) Son’s age six years ago was:

[1 mark]

• A. 11 years
• B. 3 years
• C. 5 years
• D. 15 years

Answer 1

The correct option is C 5 years

$x^2-2x-15=0$
$\Rightarrow x^2-5x+3x-15=0$
$\Rightarrow x(x-5)+3(x-5)=0$
$\Rightarrow (x-5)(x+3)=0$
$x=5$ or $-3$
Age cannot be negative.
Son’s age six years ago = 5 years