Which one of the following plots represents $f(x)=-\frac{|x|}{x}$, where $x$ is a non-zero real number?

Note: The figures shown are representative.

Five years ago, the ratio of Aman’s age to his father’s age was 1:4, and five years from now, the ratio will be 2:5. What was his father’s age when Aman was born?

For a real number $x > 1$ ,

$$ \frac{1}{\log_{2}x} + \frac{1}{\log_{3}x} + \frac{1}{\log_{4}x} = 1$$

The value of $x$ is

The greatest prime factor of $(3^{199} - 3^{196})$ is