Solve the Handshake Problem: n Couples at a Party

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Discussion Overview

The discussion revolves around a combinatorial problem involving handshakes at a party attended by n couples. Participants explore how many handshakes occur when each person shakes hands with everyone except their partner, seeking to derive a general formula for the total number of handshakes exchanged.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant asks for help with the problem of counting handshakes at a party with n couples, specifying that no one shakes hands with their partner.
  • Another participant provides a specific example with 3 couples and inquires about the total number of handshakes and how to generalize the findings.
  • Some participants calculate that each person shakes hands with 4 others and propose a method to find the total number of handshakes, suggesting a formula of 6 x 4 / 2 = 12 for the example given.
  • A participant proposes a formula of \(\frac{n\cdot (n-2)}{2}\) for the number of handshakes, where n represents the number of persons at the party.
  • Another participant corrects the previous statement, clarifying that n should represent the number of couples, leading to a revised formula of \(\frac{2n\cdot (2n-2)}{2}\) for the number of handshakes.

Areas of Agreement / Disagreement

Participants express differing views on the correct formula for calculating handshakes, with some proposing \(\frac{n\cdot (n-2)}{2}\) and others suggesting \(\frac{2n\cdot (2n-2)}{2}\). The discussion remains unresolved regarding which formula is correct.

Contextual Notes

There is a potential confusion regarding the definitions of n, whether it refers to the number of persons or the number of couples, which affects the formulation of the handshake count.

evinda
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Hello ! :)
Could you help me at the exercise below?
Suppose that n couples are at a party.
If every person at the party shake hands with any other person except from his partner, how many handshakes will have been exchanged?
 
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evinda said:
Hello ! :)
Could you help me at the exercise below?
Suppose that n couples are at a party.
If every person at the party shake hands with any other person except from his partner, how many handshakes will have been exchanged?

Hi evinda!

Suppose we have 3 couples, say persons A, a, B, b, C, and c.
How many hands does A shake?
How many handshakes are there in total?
Can you generalize?
 
"A" and "a" shake 4 hands,"B" and "b" shake 2 hands.Can you give me a hint how to find the general formula,because I have stuck?
 
evinda said:
"A" and "a" shake 4 hands,"B" and "b" shake 2 hands.Can you give me a hint how to find the general formula,because I have stuck?

Actually, "A" and "a" shake 4 hands, "B" and "b" shake 4 hands, and "C" and "c" shake 4 hands.
So there are 6 x 4 times that someone shakes a hand.
Since it takes 2 persons to do a handshake, we should divide the total number by 2.
That means that the number of handshakes is 6 x 4 / 2 = 12.

Generalize?
 
Here is an illustration.

handshake.png
 
Is it \frac{n\cdot (n-2)}{2} ,where n the number of persons that are at the party ?
 
evinda said:
Is it \frac{n\cdot (n-2)}{2} ,where n the number of persons that are at the party ?

Yep! ;)

Btw, in your problem statement, n was supposed to be the number of couples.
I'd advise against mixing up the meaning of symbols.
Your number of handshakes is \frac{2n\cdot (2n-2)}{2}, where $n$ is the number of couples.
 
Nice!Thank you very much! ;)
 

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