Solving the Combinatronics Dilemma

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In summary, the conversation discusses two different methods for finding the number of possible ways to choose 5 cards from a standard deck of 52 cards, ensuring that at least one card is chosen from each suite. The first method involves choosing one card from each suite and then one additional card from the remaining 48 cards. The second method involves choosing one card from three suites and two cards from the fourth suite, and then repeating this process for all four suites. However, the first method double counts some selections, leading to a discrepancy between the two methods.
  • #1
modulus
127
3
I solved a problem, by two different, and (apparently) viable solutions. But, each solution led me to a different answer:
The question asks me to find out the number of possible ways in which I can choose 5 cards from a standard pack of 52 cards, so that I choose at least a single card from each suite.

FIRST METHOD:
One card from each suite of 13 means a total of [13C1 * 13C1 * 13C1 * 13C1].
After that, I'll have 52-4=48 cards left from which I need to choose only one. That means 48C1.
The final result:
13C1 * 13C1 * 13C1 * 13C1 * 48

SECOND METHOD:
I'll be choosing one card from three suites, but exactly two cards from the fourth suite. So that means:
13C1 * 13C1 * 13C1 * 13C2
= 13C1 * 13C1 * 13C1 * 13C2 * (12/2)
And since I do this with each of the four suites (choose two from it only, while taking one from each of the others), I shall multiply this by 4, giving me:
13C1 * 13C1 * 13C1 * 13C2 * 24


And this is half of the answer arrived at by the first method...
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what went wrong?
 
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  • #2
In the first method you double count. For example I could have picked my cards like this:

ace of hearts, ace of spades, ace of clubs, ace of diamonds

and then the king of heartsOR

king of hearts, ace of spades, ace of clubs, ace of diamonds

and then the ace of hearts

In the first method you count those as two distinct selections even though they're the same set of five cards
 
  • #3
Oh...I see.
Thank you.
 

1. What is combinatorics?

Combinatorics is a branch of mathematics that deals with counting and arranging objects or events in a systematic way.

2. Why is solving the combinatorics dilemma important?

Solving the combinatorics dilemma is important because it helps us understand and solve various problems related to counting and arranging objects or events, which have practical applications in fields such as computer science, statistics, and physics.

3. What are some common applications of combinatorics?

Combinatorics has various applications in real-world problems, including designing efficient computer algorithms, predicting outcomes in gambling and sports, and analyzing data in genetics and epidemiology.

4. What are some key principles in solving combinatorics problems?

Some key principles in solving combinatorics problems include understanding the problem, identifying the type of problem (permutations, combinations, or arrangements), using appropriate counting techniques, and considering any restrictions or limitations.

5. How can I improve my skills in solving combinatorics problems?

To improve skills in solving combinatorics problems, it is important to practice regularly, familiarize yourself with different counting techniques, and seek help from resources such as textbooks, online tutorials, and study groups. It is also helpful to break down complex problems into smaller, manageable parts.

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