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

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.

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?

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

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

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

x = 0.5