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Homework Help: Probalitity task help.

  1. Feb 17, 2012 #1
    Let the germination probability (the probability that a seed sprouts) for seed A be Pa and B be Pb.


    a) You plant two seeds of the same kind. If you turn heads or tails of what sort you plantet, what is the probability that 2 seeds germinate?
    b) A student plant 2 seeds, but he had forgotten to note what sort of seed he had planted. What is the probability that it was A if both germinate?

    What i think i right so far:

    a) probability should be: P = (Pa^2+Pb^2)/2
     
  2. jcsd
  3. Feb 17, 2012 #2
    b) P(A|2 germinate)
    =P(2 germinate|A)P(A)/P(2 germinate)
    [tex]=\frac{\frac12P_a^2}{\frac12(P_a^2+P_b^2)}=\frac{P_a^2}{P_a^2+P_b^2}.[/tex]
     
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