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Question: Let $H$ be a graph of order 10 such that $3\le d(v)\le5$ for each vertex $v$ in $H$ [where $d(v)$ is the degree of $v$]. Not every vertex is of even degree. No two odd-degree vertices are of the same degree. What is the size [number of edges] of $H$?

Answer: Size of $H$ is 20

let $V(H)=\{{a,b,c,d,e,f,g,h,i,j\}}$, then $d(a)=3, d(b)=4, d(c)=4, d(d)=4, d(e)=4, d(f)=4, d(g)=4, d(h)=4, d(i)=4,$ $d(j)=5$


Sum is 40

hence size is 20

Am I correct?

  • 0
    a little bit more practice will clear my concepts... thank you!!!2012-07-27

1 Answers 1

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You've done all the hard work. Now all that remains is to show that such a graph exists.

Solvitur ambulando:

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