Statistics, Probability (chance of rain) problem need help

Andrew_BDK

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If there is a 60% chance of rain on Saturday and a 70% chance of rain on Sunday, then there is a 130% chance of rain over the weekend. (Select all that apply.)

A.
The chance of rain over the weekend is 70%, because it is the larger of the two chances given.
B. The chance of rain over the weekend is 65%, because it is the average of the chances of rain on Saturday and Sunday.
C. Chance is never greater than 100%.
D. The chance of rain over the weekend should be 100% because rain is always possible.
E. There is not enough information given to calculate the chance of rain over the weekend.

How many are you supposed to choose? I thought C was right but it wasn't. Anyone?
 
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That is certainly a correct choice, as it is a good reason to reject the claim. But they want you to pick all statements in the list that are true. C is not the only one.

Answers A and B are making positive claims about what the probability is. Might one of those be true? Or, if not, how about E? (I assume you recognize that D is silly.)
 
Yes, D is not correct. I am leaning towards B and C. I'm not sure if there any other ones I should select.
 
Basically, only one of A, B, and E is possible, right? No two of them can be true.

So you just have to focus on answering the question, what is the probability that there will be rain on at least one of the two days? (Notice that the first step is to clarify the question, as I have just done.)

So, if you think B is true along with C, tell me why.
 
I'm unsure about B. I thought maybe that was right because maybe that was the average length of rain per day. I know C is correct. I was unsure of the other ones.
 
Take my hint: You are trying to calculate Pr(rain on Saturday or rain on Sunday). There is no average or maximum there! How do you calculate an "or"?

But also, we know nothing at all about how long it will rain on either day, so if you had been asked for "average length of rain per day", you would have to say there was not enough information.
 
We are told that there is a 70% chance of rain on Sunday. Suppose they told you nothing about Saturday. Now what can you say about P(rains Saturday or it rains Sunday)?? Will it be exactly 70%, less than equal to 70% or greater than equal to 70%
Are the two events independant of one another? If yes, then what answer (in addition to C) should you pick?
 
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