Test series

Question

my doubt is why 14 has been subtracted ??

Comments

Spanning tree has 4 edges therefore,7C4=35

But there might be cycles of length 4 or 3,we have to calculate those

first 4 length cycles, ABCD,BCDE -->2

3 length cycles

ABC remaining edge choices 4(BE,BD,DE,CD)

BCD,4 edge choices,

BDE,4 edge choices

so 4+4+4+2=14 combinations have cycle.

35-14=21

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Thanks brother...