The probability of guessing the correct answer to . . .

Question : The probability of guessing the correct answer to a certain question is x/2. If the probability of not guessing the correct answer is 2/3, then find x.

Doubt by Saksham

Solution : 

P(Guessing the correct answer) = x/2

P(Not Guessing the correct answer) = 2/3

We know, 
P(E) + P(not E) = 1

Hence, the required value of x is 2/3.