bayes theorem

If P(A\B) = 0.6, P(B) = 0.3, P(A) = 0.2. Find P(B\A)

so then i did

\dfrac{0.2\cdot 0.6}{0.3}

to which i get out 0.4

where did i go wrong?

You're just substituting in wrong?

P(B|A) = \dfrac {P(B \cap A)} {P(A)} = \dfrac {P(B) \times P(A|B)} {P(A)}

You're just substituting in wrong?

P(B|A) = \dfrac {P(B \cap A)} {P(A)} = \dfrac {P(B) \times P(A|B)} {P(A)}

great thanks for telling me the formula in my book is wrong cheers bro

Original post by will'o'wisp2

If P(A\B) = 0.6, P(B) = 0.3, P(A) = 0.2. Find P(B\A)

so then i did

\dfrac{0.2\cdot 0.6}{0.3}

to which i get out 0.4

where did i go wrong?

Bayes' Theorem states that

\displaystyle P(A|B)=\frac{P(B|A)P(A)}{P(B)}

.

So, swap A and B around to get

\displaystyle P(B|A)=\frac{P(A|B)P(B)}{P(A)}

. You have substituted wrong, as you can see.

Bayes' Theorem states that

\displaystyle P(A|B)=\frac{P(B|A)P(A)}{P(B)}

.

So, swap A and B around to get

\displaystyle P(B|A)=\frac{P(A|B)P(B)}{P(A)}

. You have substituted wrong, as you can see.

fantastic thank you

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