Help Me Out With These 2 Tough Questions

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Discussion Overview

The discussion revolves around two mathematical problems involving the Well-Ordering Principle and a combinatorial argument related to friendships among students. The first question asks for a proof using the Well-Ordering Principle, while the second question seeks to demonstrate that at least two students in a class have the same number of friends.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants suggest using the Well-Ordering Principle to find the smallest number in a set of possible remainders for the first question.
  • One participant argues that the second problem is false unless it is assumed that each person has at least one friend.
  • Another participant counters that the second problem can be solved without additional assumptions, provided that friendship is mutual and no one is their own friend.
  • Hints are provided regarding the application of the Pigeonhole Principle and the generality of the number of students involved in the second problem.
  • Participants emphasize the need to show the uniqueness of the remainders and quotients in the first problem, although one participant expresses uncertainty about needing to prove uniqueness.

Areas of Agreement / Disagreement

There is disagreement regarding the assumptions necessary for the second problem, particularly about whether each student must have at least one friend. The first problem appears to be more straightforward, but participants have varying levels of familiarity with the Well-Ordering Principle.

Contextual Notes

Participants express uncertainty about the uniqueness of the remainders and quotients in the first problem and the assumptions required for the second problem, indicating that these aspects may need further clarification.

evanx
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Please help me out!


Q1
m, n are natural numbers (which include zero for the sake of this question) and n =/= 0, then there are natural numbers q and r such that m= qn + r and r < n. Use the Well-Ordering Principle to prove this fact.

Q2
There are 51 students in a class. Prove there are at least two students with exactly the same number of friends.
 
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the well orderin principle says there is a smallest number of a certain type. So in this problem look for the desired number which is supposed to be small. take all numbers like it and among them take the smallest one and see if it is small enough to work for you.

problem 2 is false without assuming each person has at least one friend.
 
what have you done so far? the first one is a pretty straightforward application of the wop. you've got a set of possible r's which is a subset of N... do i need to say the rest? then you need to show that the smallest element is the "right size", and that yer r & q are unique (uniqueness should be pretty routine, even for a beginner - it's done like every other uniqueness proof)
 
hmm... I think problem 2 is just fine without any added assumption. Well you have to assume friendship is mutual. If a is a friend of b then b is a friend of a. And no one is their own friend. But these are reasonable assumptions. So my two big hints are: 1)there is nothing special about 51, any number will do, and 2) the pigeon hole principle. So try the same question with 3,4,5 students.

Hope that helps,
Steven
 
fourier jr said:
what have you done so far? the first one is a pretty straightforward application of the wop. you've got a set of possible r's which is a subset of N... do i need to say the rest? then you need to show that the smallest element is the "right size", and that yer r & q are unique (uniqueness should be pretty routine, even for a beginner - it's done like every other uniqueness proof)

I have got Q2 (sort of...) but am at a loss for Q1 since I am unfamiliar with the Well-ordering principle. I do not have to prove uniqueness of r and q though (I think).
 

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