Question:
The sum of the reciprocals of Meena's ages (in years) 3 years ago and 5 years hence is $\frac{1}{3}$. Find her present age.
Solution:
Let the present age of Meena be x years.
Meena's age 3 years ago = (x − 3) years
Meena's age 5 years hence = (x + 5) years
According to the given condition,
$\frac{1}{x-3}+\frac{1}{x+5}=\frac{1}{3}$
$\Rightarrow \frac{x+5+x-3}{(x-3)(x+5)}=\frac{1}{3}$
$\Rightarrow \frac{2 x+2}{x^{2}+2 x-15}=\frac{1}{3}$
$\Rightarrow x^{2}+2 x-15=6 x+6$
$\Rightarrow x^{2}-4 x-21=0$
$\Rightarrow x^{2}-7 x+3 x-21=0$
$\Rightarrow x(x-7)+3(x-7)=0$
$\Rightarrow(x-7)(x+3)=0$
$\Rightarrow x-7=0$ or $x+3=0$
$\Rightarrow x=7$ or $x=-3$
∴ x = 7 (Age cannot be negative)
Hence, the present age of Meena is 7 years.