Bayes’ Theorem – The probability Event A will happen given Event B Happened

Bayes’ Theorem – Is the probability Event A will happen given (|)  Event B happened.

P(A|B) = P(B|A) * P(A) / P(B)

For example (Assume we have 3 out of 4 probabilities):

Calculate a probability that an event A(Eating) will happen given (|) that an event B(Exercising) happened.

P(A|B) = P(B|A) * P(A) / P(B)

A =   Eating

B =  Exercising

P(A|B) = P(Eating given that Exercising  happened)  = (The Unknown)

P(B|A)  =P(Exercising given that  Eating happened) = 30%

P(A) = P(Eating) = 80%

P(B) = P(Exercising) = 50%

So, P(B|A) * P(A) / P(B) = 30%*80%/50% = 24%/50% = 48%

P(A|B) = 48%

Eating will happen 48% of the times given (|)  that an  event Exercising happened.