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

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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

0
17 years ago
#2
(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

lol, and your doing a maths degree at Sheffield.
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#3
(Original post by Bhaal85)
lol, and your doing a maths degree at Sheffield.
Yes and I never did stats in maths, not very helpful.....
0
17 years ago
#4
(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

isnt it 0.6/0.7?
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#5
(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...

0
17 years ago
#6
(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...

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

x = 0.5
0
17 years ago
#7
0.7.

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

Jonny W.
0
17 years ago
#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

Does either also mean both?
0
17 years ago
#9
(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

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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