The probability of guessing the correct answer to a certain question is $\frac{x}{2}$. If the probability of not guessing the correct answer to the question is $\frac{2}{3}$ , then $x$ is:

The correct option is D. $\frac{2}{3}$

The probability of guessing the correct answer to certain question is $\frac{x}{2}$.

The probability of not guessing the correct answer to same question is $\frac{2}{3}$.

Now, we know that,

$P$(happening of an event) $+$ $P$(not happening of an event) $=1$

$\therefore P$(guessing the correct answer) $+$ $P$(not guessing the correct answer) $=1$

$\Rightarrow \frac{x}{2}+\frac{2}{3}=1$

$\Rightarrow \frac{x}{2}=1-\frac{2}{3}=\frac{1}{3}$

$\Rightarrow x=\frac{2}{3}$

Hence, $x=\frac{2}{3}$