Marginal and Conditional Probabilities



What are the chances of choosing grape?


Def: Marginal Probability—the probability of a single event without consideration of any other event.


Def: Conditional Probability—the probability that an event will occur given that another event has already occurred.


            --probability of A given that B has occurred


Compute with Class Grape Data          



Row by Window

Middle Row

Row by Door







Not Grape












P(middle row) = ?

P(not grape) = ?

P(not grapemiddle row)

P(middle rownot grape)




**Monty’s Dilemma**