Part (a) Finding the probability of either A or B
We are told that events A and B are mutually exclusive. This means they cannot happen at the same time. We can say P(A and B) = 0
Furthermore,
P(A or B) = P(A) + P(B) - P(A and B)
P(A or B) = 0.4 + 0.2 - 0
P(A or B) = 0.6
<h3>Answer: 0.6</h3>
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Part (b) Finding the probability of neither A nor B
P(A or B) + P(neither A nor B) = 1
P(neither A nor B) = 1 - P(A or B)
P(neither A nor B) = 1 - 0.6
P(neither A nor B) = 0.4
The reason why this works is to imagine throwing a dart at the Venn diagram. You'll either...
- you land in A or B (pick one but not both), OR,
- you'll land outside both regions A and B.
One or the other must happen. Both events cannot happen simultaneously.
<h3>Answer: 0.4</h3>
