Given two events A and B, if the odds against A are 2 to 1 those in favour of AUB are 3 to 1, then
13≤P(B)≤12
12≤P(B)≤34
512≤P(B)≤34
0≤P(B)≤1
Given that
P(A¯):P(A)=2:1⇒P(A¯)=23,P(A)=13P(A∪B):P(A∪B¯)=3:1⇒P(A∪B)=34,P(A∪B¯)=14P(A∪B)−P(A)≤P(B)≤P(A∪B)⇒512≤P(B)≤34