# GATE2015-3-40

33 votes
3.6k views
Let $G$ be a connected undirected graph of $100$ vertices and $300$ edges. The weight of a minimum spanning tree of $G$ is $500$. When the weight of each edge of $G$ is increased by five, the weight of a minimum spanning tree becomes ______.

edited

## 4 Answers

55 votes

Best answer
First find no of edges in mst.
Mst has $n-1$ edges where $n$ is no of vertices. $100-1 =99$ edges
Each $99$ edges in mst increases by $5$ so weight in mst increased $99*5=495$
Now total weight of mst $=500+495=995$

edited
1
In question 300 edges given what does that statement say ? I didn't get it ?
4
The total number of edges present in a graph is 300.

But as we know that the minimum number of edges required in a minimal connected single component graph is n-1.
10 votes
No of edges =99 , now mention condition 99*5 = 495+500 = 995
4 votes
Since there are 100 vertices, there must be 99 edges in Minimum Spanning Tree (MST). When weight of every edge is increased by 5, the increment in weight of MST is = 99 * 5 = 495 So new weight of MST is 500 + 495 which is 995
0 votes

Adding or multiplying all the edges of an MST by a constant does not change the MST, it only changes the value of MST.

Vertices = 100.

Hence, edges in the MST = 99.

Weight = 500

Since the MST would remain the same; just the edge weights would be upgraded by 5, upgraded MST weight:

$500+99(5)=995$

Answer:

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