For two events A and B in a sample space, P(A)=0.5, P(B)=0.4 and P(A∪B)=0.9. Which one of the following statements is true?
a) P(A∩B)=0.9,so A and B are identical events.
b) P(A∩B)=0.2,assuming A and B are independent.
c) P(A∩B)=0,so A and B are mutuallyexclusive.
d) P(A∩B)=0.1,so A and B overlap.