Zhi went to a blackjack table at the casino At this table th

Zhi went to a blackjack table at the casino. At this table, the dealer is using one standard deck of 52 cards that has just been shuffled. Zhi knows that getting 21, a blackjack, is the best hand possible. She really likes when she is dealt an ace first. The first card is dealt to her and in split second she can see it is not face card but is unsure if it is an Ace or not.

What is the probability it is a Ace, given that it is not a face card?

Solution

p ( it is a ace | it is not a face card) = P ( it is an ace and it is not a face card) / p ( it is not a face card)
= (4 / 52) / ( 40 / 52 ) = 0.1...