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    Pretty sure this is fairly simple and I'm just being a total idiot right now as I haven't done probability in ages, but can someone help me with this:

    "Suppose that I think the probability that a certain particle exists is 0.2. Furthermore my theory tells me that if the particle exists the probability that a certain experiment succeeds is 0.8, whereas if the particle doesn't exist the probability of success is 0.05. The experiment does succeed. How probable should I think it that the particle exists now?"

    How do I work out what the probability of the experiment succeeding, period, given nothing, is?
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    (Original post by TorpidPhil)
    Pretty sure this is fairly simple and I'm just being a total idiot right now as I haven't done probability in ages, but can someone help me with this:

    "Suppose that I think the probability that a certain particle exists is 0.2. Furthermore my theory tells me that if the particle exists the probability that a certain experiment succeeds is 0.8, whereas if the particle doesn't exist the probability of success is 0.05. The experiment does succeed. How probable should I think it that the particle exists now?"

    How do I work out what the probability of the experiment succeeding, period, given nothing, is?
    If E is the event "the particle exists" and X is the event "the experiment succeeds" then what you have been given is P(E), P(X|E) and P(X| ~E). You should now be able to work out P(X) by using the law of total probability.
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    (Original post by Gregorius)
    If E is the event "the particle exists" and X is the event "the experiment succeeds" then what you have been given is P(E), P(X|E) and P(X| ~E). You should now be able to work out P(X) by using the law of total probability.
    Yeah, that's what I can't do because I suck at probability and it is making my mind trip up for no apparent reason :P
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    (Original post by torpidphil)
    yeah, that's what i can't do because i suck at probability and it is making my mind trip up for no apparent reason
    p(x) = p(x|e)p(e) + p(x|~e)p(~e)
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    (Original post by Gregorius)
    p(x) = p(x|e)p(e) + p(x|~e)p(~e)
    Than you sir
 
 
 
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