Full house hand

In the game of poker, a full house is a special kind of 5-card hand. It consists of 3 cards of the same rank and another 2 cards of the same rank.

If a player is dealt 5 cards from a shuffled 52-card poker deck, what is the probability of getting a full house? Round the answer to six decimal places.

0.000002 0.000002 0.051501 0.051501 0.001441 0.001441 0.000360 0.000360

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2 solutions

Andy Hayes
Jun 10, 2016

The probability is:

( 13 1 ) ( 4 3 ) ( 12 1 ) ( 4 2 ) ( 52 5 ) = 3744 2598960 0.001441 \frac{\binom{13}{1}\binom{4}{3}\binom{12}{1}\binom{4}{2}}{\binom{52}{5}}=\frac{3744}{2598960}\approx \boxed{0.001441}

The denominator is a count of the number of ways to select 5 5 cards from a set of 52 52 : ( 52 5 ) \binom{52}{5}

The numerator can be interpreted as follows:

First, choose 1 1 rank from among the 13 13 : ( 13 1 ) \binom{13}{1}

Then, choose 3 3 cards from among the 4 4 cards of that rank: ( 4 3 ) \binom{4}{3}

Next, choose another 1 1 rank from the remaining 12 12 ranks: ( 12 1 ) \binom{12}{1}

Finally, choose 2 2 cards from among the 4 4 cards of that rank ( 4 2 ) \binom{4}{2}

Then, use the rule of product to find the total number of distinct hands which are full houses.

Can you more explain the product of numerator

mongol genius - 4 years, 9 months ago

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The numerator is all about counting the number of combinations of cards that are full house hands . The binomial coefficient is used to count.

( 13 1 ) \binom{13}{1} means that 1 1 of the ranks is chosen from among the 13 13 . There are ( 13 1 ) = 13 \binom{13}{1}=13 ways to choose a rank in this way. You don't really need the binomial coefficient to know that there are 13 ways to choose a rank, but it's helpful in this context to understand how the binomial coefficient works.

( 4 3 ) \binom{4}{3} means that 3 3 of the suits are chosen from among the 4 4 . There are ( 4 3 ) \binom{4}{3} ways to choose suits in this way. These ways are:

( , , ) ( , , ) ( , , ) ( , , ) \begin{array}{cc} (\heartsuit,\ \diamondsuit,\ \clubsuit) & (\heartsuit,\ \diamondsuit,\ \spadesuit) \\ (\heartsuit,\ \clubsuit,\ \spadesuit) & (\diamondsuit, \clubsuit,\ \spadesuit) \end{array}

These selections are independent, so there are ( 13 1 ) ( 4 3 ) = 52 \binom{13}{1}\binom{4}{3}=52 combinations of 3 cards of the same suit.

The selection of the 2-of-a-kind is similar, but now there are only 12 ranks left to choose from.

Andy Hayes - 4 years, 8 months ago

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Wonderful explain! Thanks.

Madhu . - 2 years, 11 months ago

I was trying to do 3/51 * 2/50 * 48/49 * 3/48, but that means drawing the cards in the order AAABB, when in fact the order doesn't matter (i.e. BBAAA works too). This actually makes my solution smaller by exactly a factor of 10, which was driving me nuts.

Win Wang - 3 years, 3 months ago

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I was stuck in the exact same position. I totally forgot that order didn't matter at all. Damn it!

Madhu . - 2 years, 11 months ago

I did the same thing. Its 10^-4

Hafiz muhammad Ibrahim jaffar - 11 months, 1 week ago

P ( Full House ) = 13 P 2 . 4 C 3 . 4 C 2 52 C 5 = 0.001441 P(\text{Full House}) = \dfrac{\textcolor{#3D99F6}{^{13}P_2} . \textcolor{#CEBB00}{^4C_3} . \textcolor{#D61F06}{^4C_2}}{\textcolor{#20A900}{^{52}C_5}} = \boxed{0.001441}

Selecting any 2 ranks \textcolor{#3D99F6}{\text{Selecting any 2 ranks}}

Choosing 3 out of 4 cards \textcolor{#CEBB00}{\text{Choosing 3 out of 4 cards}}

Choosing 2 out of 4 cards \textcolor{#D61F06}{\text{Choosing 2 out of 4 cards}}

Choosing 5 out of 52 cards \textcolor{#20A900}{\text{Choosing 5 out of 52 cards}}

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