AchyuthReddy wrote:

How many diagonals are there in an octagon?

A)56

B)28

C)20

D)16

E)8

Let's examine ONE vertex in an octagon (an 8-sided polygon)

We can draw 5 diagonal lines from that one vertex

So, each of the 8 vertices can have 5 diagonal lines

So, the total number of diagonal lines = (8)(5) =

40But wait!!

We have inadvertently counted every diagonal TWICE.

For example, we counted the diagonal from vertex A to vertex B AND we counted the diagonal from vertex B to vertex A

So, to account for this DUPLICATION, we must divide

40 by 2 to get

20Answer: C

Cheers,

Brent

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Brent Hanneson – Creator of greenlighttestprep.com

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