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Michigan State University
Sara U. Calculus 3 1 year, 2 months ago
A standard deck of playing cards has 52 cards. a. How many different 5 -card poker hands could be formed from a standard deck? b. How many different 13 -card bridge hands could be formed? c. How can you tell that numbers of combinations are being asked for, not numbers of permutations? Check my profile and contact me for one on one online tutoring.
P card 1 being a heart is 13/52. P card 2 being a heart (there's one less card, and one less heart) is 12/51 P card 3: 11/50 P card 4: 10/49 P card 5: 9/48 The probability of all five events is the product of their probabilities: 13/52 * 12/51 * 11/50 * 10/49 * 9/48 = 0.000495198079231693.
The question is:
The answer is $\frac{52P5}{(5!)^5}$ or $\frac{52!}{47!5!}$ I understand the reason after seeing the answer: $25$ ordered cards are picked from the deck of $52$, then divided by the number of ways each hand can be ordered, because the order of a hand does not matter. However, before seeing the answer I came up with this attempt: You choose $5$ cards from $52$, the order doesn't matter so we have $52\choose{5}$. Then you're left with $47$ cards and for the next hand we have $47\choose{5}$. The final sum is ${{52}\choose{5}} + {{47}\choose{5}} + {{42}\choose{5}} + {{37}\choose{5}} + {{32}\choose{5}}$. This sum is considerably larger, but while I understand the reason $\frac{52!}{47!5!}$ is the correct, I can't find the mistake in my first attempt. |