maggiehodgson
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P(A) =0.48 P(B)= 0.64 P(AnB) - 0.13

I did a table for this and got the same answers as the book for the following P(AuB), P(B'), P(AnB') but for P(AuB') I got 0.49 and the book says it's 0.36. Isn't it P(A) + P(B')- P(AnB')? If not, why does the rest of my table work?
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ghostwalker
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(Original post by maggiehodgson)
P(A) =0.48 P(B)= 0.64 P(AnB) - 0.13

I did a table for this and got the same answers as the book for the following P(AuB), P(B'), P(AnB') but for P(AuB') I got 0.49 and the book says it's 0.36. Isn't it P(A) + P(B')- P(AnB')? If not, why does the rest of my table work?

Agree with your answer. The book cannot be correct since P(AuB') >= P(A) = 0.48. Ergo, book is @%#&"
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maggiehodgson
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(Original post by ghostwalker)
Agree with your answer. The book cannot be correct since P(AuB') >= P(A) = 0.48. Ergo, book is @%#&"
Thank you. What would I do without TSR!
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ghostwalker
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(Original post by maggiehodgson)
Thank you. What would I do without TSR!
You're welcome.

Notice the reasoning in my post:

The probability of the union of two (or more) events is greater than or equal to the probability of either event by itself.

You can use this as a confidence check. If your result fails that test, then you know there's something wrong. If it doesn't fail it of course then it tells you nothing about the correctness of your working.
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maggiehodgson
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(Original post by ghostwalker)
You're welcome.

Notice the reasoning in my post:

The probability of the union of two (or more) events is greater than or equal to the probability of either event by itself.

You can use this as a confidence check. If your result fails that test, then you know there's something wrong. If it doesn't fail it of course then it tells you nothing about the correctness of your working.
Oh yes.
Not only do I have the edexcel yr2 A level book but also the AQA one. They both seem to be error prone. I suppose that because I bought them as soon as they came out they hadn't been tested thoroughly. Perhaps future editions will be better. Always an optimist.
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