Question

The probability of guessing the correct answer to certain question is X/2. if probability of not guessing the correct answer is 3x/2, then find X.

Answer 1

We know that P(E)+P(E¹)=1
So,x/2+3x/2=1
⇒4x/2=1
⇒4x=2
⇒x=2/4
⇒x=1/2

Answer 2

So, the probability of any event = 1.

1 = x/2 + 3x/2
1 = 4x/2
1 × 2 = 4x 
x = 2/4
x = 0.5

So, x = 0.5 or x = 1/2.