Hi there, just wanted to let you know that there’s a typo in the 3rd ex of PrepSwift: A OR B (Independent).

“Events A and B are independent. If P(B)−P(A)=0.3 and the probability that A or B occur together is 0.82, what is P(A)?”

It should be 0.28 to give the suggested answer. Take care!

No, P(A) is 0.4 indeed. Notice that

P(A \cup B) = P(A) + P(B) - P(A)P(B)

If P(A) = 0.4, P(B) = 0.7, we get P(A \cup B) = 0.4 + 0.7 - 0.28 = 0.82.

I got 0.4 indeed. However, what I’m confused about is the wording. As I understand it “occurring together” means P(A) * P(B). That’s why I thought AB = 0.28. I would consider removing the word “together”, unless it’s how GRE phrases it as well.

Got it - the wording has been fixed.

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