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Prove that a tree with Delta(T)=k (Delta means maximum degree) has at least k vertices of degree 1.

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I don't understand how you count the degree of the vertices.

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2.- Prove that a tree with Delta(T)=k ( Delta means maximum degree) has at least k vertices of degree 1.

Proof. We prove it by contradiction. Suppose that and there are s vertices of degree 1, where s<k. By a theorem , we know that

Note: To count , we know that there is at least one vertex with maximum degree k; and there are s vertices with degree 1, so the rest of |V(T)|-s-1 vertices have degrees at least 2. Hence, we have
(Why happened this I don't understand this inequality can you explain this better, can you make a graph)

So,

As s<k, we know that . Hence,

which is a contradiction, since |E(T)|=|V(T)|-1 for tree T. We complete the proof

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This solution is comprised of a detailed explanation to prove that a tree with Delta(T)=k (Delta means maximum degree) has at least k vertices of degree 1.

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  • BSc , Wuhan Univ. China
  • MA, Shandong Univ.
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  • "Your solution, looks excellent. I recognize things from previous chapters. I have seen the standard deviation formula you used to get 5.154. I do understand the Central Limit Theorem needs the sample size (n) to be greater than 30, we have 100. I do understand the sample mean(s) of the population will follow a normal distribution, and that CLT states the sample mean of population is the population (mean), we have 143.74. But when and WHY do we use the standard deviation formula where you got 5.154. WHEN & Why use standard deviation of the sample mean. I don't understand, why don't we simply use the "100" I understand that standard deviation is the square root of variance. I do understand that the variance is the square of the differences of each sample data value minus the mean. But somehow, why not use 100, why use standard deviation of sample mean? Please help explain."
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