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Probability questions

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Probability questions

Post  Admin on Sun Jan 02, 2011 10:00 pm

Enjoy



Answers with explaination please!

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Re: Probability questions

Post  Thimodya/Waspinator on Wed Jan 05, 2011 8:21 am

I think the answer is 6.5
because if the probability of obtaining A is 0.5 and obtaining B is 0.35 and the probability of obtaining neither's intersection is o.2
then 0.5 - 0.2 is 0.3 and 0.35- 0.2 is 0.15
and 0.15 + 0.5 is 0.65 and 0.3+0.35 is also 0.65...................right?

someone please help me this is confusing
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Re: Probability questions

Post  Federico on Fri Jan 07, 2011 9:09 pm

I think that it's 0.45.
I did the same thing as Timmy, but instead I added 0.3 to 0.15.

But it could be 0.2.
Neither's intersection is the middle bit, isn't it. So it would be 0.2

So confused

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Re: Probability questions

Post  fergus on Sat Jan 08, 2011 1:22 am

Federico wrote:I think that it's 0.45.
I did the same thing as Timmy, but instead I added 0.3 to 0.15.

But it could be 0.2.
Neither's intersection is the middle bit, isn't it. So it would be 0.2

So confused
freddy i dont think A'∩B' is the middle section. Mr safdar wouldnt give us a question with the answer writen in front of us.
im not too sure if 0.3 to 0.15s wrong though
so i also think its 0.45




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Re: Probability questions

Post  Luka a.k.a GodOfRandom on Sat Jan 08, 2011 2:03 am

fergus wrote:
Federico wrote:I think that it's 0.45.
I did the same thing as Timmy, but instead I added 0.3 to 0.15.

But it could be 0.2.
Neither's intersection is the middle bit, isn't it. So it would be 0.2

So confused
freddy i dont think A'∩B' is the middle section. Mr safdar wouldnt give us a question with the answer writen in front of us.
im not too sure if 0.3 to 0.15s wrong though
so i also think its 0.45

not bad fergus but thats not a good hidden message and i think that A'∩B' is anything that is not A intersects with anything that is not B so the entire outside of both circles

we want to find where A and B both occur so what we want is the probability of A∩B however where i am having trouble finding that.




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Re: Probability questions

Post  Jihye Choi on Sat Jan 08, 2011 6:01 am

I think the answer is 0.05

because [p(A'∩B') = 0.2] is the probability of obtaining neither's intersection,
and we want to find p(A and B), middle section.
p(A) = 0.5 , p(B) = 0.35 , p(A'∩B') = 0.2 , and I think E = 1

E - p(A'∩B') = p(A∪B)
1 - 0.2 = 0.8 -----------------> so, p(A∪B) = 0.8

p(A∪B) = p(A) + p(B) - p(A∩B)
0.8 = 0.5 + 0.35 - p(A∩B)
∴ p(A∩B) = 0.5 + 0.35 - 0.8 = 0.05



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Well done

Post  Admin on Sun Jan 09, 2011 1:51 am

Well done Rachel. 0.05 is correct.

If you want to find the answer in terms of areas- the area inside the circles has to be 0.8. P(a)+P(b)=0.85 therefore we have 0.05 extra or counted twice.

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