In: Math
1.11. Problem. (Sections 2.2-2.4, 3.1) Five cards are drawn from a standard deck of 52 cards.
(a) Given that exactly three of the five cards show a hearts suit, calculate the probability that the hand also includes a three-of-a-kind.
(b) Given that the five card hand contains a three-of-kind, find the probability that it contains at three hearts.
As per my knowledge of cards a three-of-a-kind means cards of same denominations.
P[ 5 out of 3 cards are heart ] = 13C3*39C2 ( 3 heart cards and 2 any other cards )
P[ a three-of-a-kind ] = 13*4C3*48C2 ( 3 cards from any 4 cards of same denomination and 2 cards from other 48 cards , also multiplies by 13 because there are 13 options for the card to be chosen )
P[ 5 out of 3 cards are heart and a three-of-a-kind ] = 3*13C3*3C2 ( any 3 heart and out of those 3 only any one card is repeated twice )
a) Given that exactly three of the five cards show a hearts suit, calculate the probability that the hand also includes a three-of-a-kind.
P[ a three-of-a-kind | 5 out of 3 cards are heart ] = P[ 5 out of 3 cards are heart and a three-of-a-kind ] / P[ 5 out of 3 cards are heart ] = 3*13C3*3C2 / 13C3*39C2 = 3*3C2 / 39C2 = 9/741 = 0.0121
P[ a three-of-a-kind | 5 out of 3 cards are heart ] = 0.0121
b) (b) Given that the five card hand contains a three-of-kind, find the probability that it contains at three hearts
P[ 5 out of 3 cards are heart | a three-of-a-kind ] = P[ 5 out of 3 cards are heart and a three-of-a-kind ] / P[ a three-of-a-kind ] = 3*13C3*3C2 / 13*4C3*48C2 = 3*3*286 / 13*4*1128 = 2574 / 58656 = 0.0439
P[ 5 out of 3 cards are heart | a three-of-a-kind ] = 0.0439