A full joint distribution for the Toothache, Cavity and Catch is given in the…

2018

A full joint distribution for the Toothache, Cavity and Catch is given in the table below

What is the probability of Cavity, given evidence of Toothache?

Answer: D. ⟨0.6,0.4⟩Compute P(Cavity | Toothache) = P(Cavity and Toothache) / P(Toothache). P(Cavity and Toothache) = 0.108 + 0.012 = 0.12. P(Toothache) = 0.108 + 0.012 + 0.016 +…

  1. A.

    ⟨0.2,0.8⟩

  2. B.

    ⟨0.4,0.8⟩

  3. C.

    ⟨0.6,0.8⟩

  4. D.

    ⟨0.6,0.4⟩

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Correct answer: D

Compute P(Cavity | Toothache) = P(Cavity and Toothache) / P(Toothache).

  • P(Cavity and Toothache) = 0.108 + 0.012 = 0.12.

  • P(Toothache) = 0.108 + 0.012 + 0.016 + 0.064 = 0.20.

  • Therefore P(Cavity | Toothache) = 0.12 / 0.20 = 0.6.

So the posterior distribution over Cavity given Toothache is ⟨0.6, 0.4⟩ (Cavity = true, Cavity = false).

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