Given: P(A or B) = 0.7, P(A and B) = 0.3 and P(bar A) = 0.4
We know, P(A) = 1 – P(bar A)
= 1 – 0.4 = 0.6
So, P(A) = 0.6
Again, P(A or B) = P(A) + P(B) – P(A and B)
By substituting values in the above formula, we get
0.7 = 0.6 + P(B) – 0.3
0.7 = 0.3 + P(B)
0.7 – 0.3 = P(B)
Or P(B) = 0.4