## mandja 3 years ago Hey, guys, I was wondering if you could help me with some statistics and physics. http://www.trin.cam.ac.uk/show.php?dowid=475 Questions 2, 4, 5, 6, 9 and 10. Thank you :)

1. Youngster

for number two, make a "tree" i guess, it might help. sorry, im still learning statistics there is a formula for how to find the probablity of B given A, but I can't seem to get it on here. :(

2. mandja

Thanks nonetheless... :)

3. vf321

@mandja for #2 what is the probability for a false positive? Are we to assume it is zero?

4. vf321

Assuming that the test is 95% accurate for the positive and for 100% accurate for the negative, this is solvable: Let $$C$$ denote having the condition and positive/negative signs denote the results. Given is this: $P(C)=0.001$$P(+|C) = 0.95$$P(\lnot C)=1-P(C) = 0.999$$P(+|\lnot C)=P(\lnot C\land+)/P(\lnot C)=0.05$Then,$P(C|+)=\frac{P(+\land C)}{P(+)}$Since $$P(+) = P(+|\lnot C)P(\lnot C) + P(+|C)P(C)$$, we can just plug in the values to get: 1.8%

5. mandja

Thanks. For the 4-th question I'm thinking of binomial distribution?