Jane Street–styleTraderTradingQuestion #447

You are going camping over the weekend. There is a 50% chance of rain on Saturday and a 60% chance on Sunday. What is the probability that you will not experience rain? (You are not told whether the days are independent, so consider this in your answer.) Then, after giving your answer, assume the probabilities are not independent and are positively correlated. Will the chance of having a 'dry' weekend increase or decrease?

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State the assumptions, try a simple case, then work toward a general solution. Check the result and explain how it changes if an assumption changes.

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