Nice easy stats which I've never understood...

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byb3
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#1
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#1
A student is taking two classes, psychology and statistics. If the probability that he will pass either of the courses is 0.8, that he will pass both courses is 0.6, and he will fail in psychology is 0.3, find the probability that:

a) he will pass psychology
b) he will pass statistics

Now I am assuming the answer to the first is simply 1-P(FAIL IN PSYCH) = 1 - 0.3 = 0.7

However the answers I have got for statistics don't really work. So can anybody explain how?

TIA

Adam
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Bhaal85
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(Original post by byb3)
A student is taking two classes, psychology and statistics. If the probability that he will pass either of the courses is 0.8, that he will pass both courses is 0.6, and he will fail in psychology is 0.3, find the probability that:

a) he will pass psychology
b) he will pass statistics

Now I am assuming the answer to the first is simply 1-P(FAIL IN PSYCH) = 1 - 0.3 = 0.7

However the answers I have got for statistics don't really work. So can anybody explain how?

TIA

Adam
lol, and your doing a maths degree at Sheffield.
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byb3
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(Original post by Bhaal85)
lol, and your doing a maths degree at Sheffield.
Yes and I never did stats in maths, not very helpful.....
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elpaw
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(Original post by byb3)
A student is taking two classes, psychology and statistics. If the probability that he will pass either of the courses is 0.8, that he will pass both courses is 0.6, and he will fail in psychology is 0.3, find the probability that:

a) he will pass psychology
b) he will pass statistics

Now I am assuming the answer to the first is simply 1-P(FAIL IN PSYCH) = 1 - 0.3 = 0.7

However the answers I have got for statistics don't really work. So can anybody explain how?

TIA

Adam
isnt it 0.6/0.7?
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byb3
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(Original post by elpaw)
isnt it 0.6/0.7?
thats what I thought, but then how does the probability that he passes either course = 0.8 work...

because you have 6/7*0.3 + 1/7*0.7 = 0.36 ...not 0.6?

Of course I could be going off on a tangent here...

Adam
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elpaw
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#6
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(Original post by byb3)
thats what I thought, but then how does the probability that he passes either course = 0.8 work...

because you have 6/7*0.3 + 1/7*0.7 = 0.36 ...not 0.6?

Of course I could be going off on a tangent here...

Adam
P(A or B) = P(A) + P(B) - P(A and B)
0.8 = x + 0.7 - 0.6

x = 0.5
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Jonny W
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0.7.

Draw a two-circle Venn diagram, put 0.6 in the intersected part, ...

Jonny W.
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Juwel
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#8
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#8
(Original post by byb3)
A student is taking two classes, psychology and statistics. If the probability that he will pass either of the courses is 0.8, that he will pass both courses is 0.6, and he will fail in psychology is 0.3, find the probability that:

a) he will pass psychology
b) he will pass statistics

Now I am assuming the answer to the first is simply 1-P(FAIL IN PSYCH) = 1 - 0.3 = 0.7

However the answers I have got for statistics don't really work. So can anybody explain how?

TIA

Adam
Does either also mean both?
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Bigcnee
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#9
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(Original post by elpaw)
P(A or B) = P(A) + P(B) - P(A and B)
0.8 = x + 0.7 - 0.6

x = 0.5
Correct but you added wrong.

P(S) = 0.7

because

P(S) = P(P U S) - P(P) + P(P n S)

where P(P) = 1 - P(Pcomp.)

P = Event pass Psychology
S = Event pass statistics
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