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.comSign up for GRE Question of the Day emails