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A certain game board is in the shape of a non-convex [#permalink]
20 Dec 2006, 14:41

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B

C

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Difficulty:

45% (medium)

Question Stats:

46% (02:36) correct
54% (01:50) wrong based on 37 sessions

A certain game board is in the shape of a non-convex polygon, with spokes that extend from each vertex to the center of the board. If each spoke is 8 inches long, and spokes are used nowhere else on the board, what is the sum of the interior angles of the polygon?

(1) The sum of the exterior angles of the polygon is 360º.

(2) The sum of the exterior angles is equal to five times the total length of all of the spokes used.

from 2
The sum of the exterior angles is equal to five times the total length of all of the spokes used.
Let say Y= # of sides and Y sum of interior angles
for any type of polygon the interior angle and exterior angle always add to 180Â°.

5*8*N + Y = 180*N
=>40N+Y = 180 N
and
Y = (N-2)*180

from 2 The sum of the exterior angles is equal to five times the total length of all of the spokes used. Let say Y= # of sides and Y sum of interior angles for any type of polygon the interior angle and exterior angle always add to 180Â°.

5*8*N + Y = 180*N =>40N+Y = 180 N and Y = (N-2)*180

N = 9 and Y =(9-2)*180= 7*180 So B whats the OA?

But How did you get N=9 ?

40N+Y = 180 N ------ sum of exterior angles + sum of interior angles
Y = (N-2)*180 --------sum of interior angles

The formula for the sum of the interior angles of a non-convex polygon is (n â€“ 2)(180), where n represents the number of sides. To find the sum of the interior angles of the polygon then, we need to know the number of sides. We can therefore rephrase the question:

How many sides does the game board have?

(1) INSUFFICIENT: It tells us nothing about the number of sides. The sum of the exterior angles for any non-convex polygon is 360.

(2) SUFFICIENT: The sum of the exterior angles = 5 Ã— length of each spoke Ã— number of spokes.

360 = 5(8)(x)
360 = 40x
9 = x

The game board has nine sides. The sum of its interior angles is (9 â€“ 2)(180) = 1260.

The formula for the sum of the interior angles of a non-convex polygon is (n â€“ 2)(180), where n represents the number of sides. To find the sum of the interior angles of the polygon then, we need to know the number of sides. We can therefore rephrase the question:

How many sides does the game board have?

(1) INSUFFICIENT: It tells us nothing about the number of sides. The sum of the exterior angles for any non-convex polygon is 360.

(2) SUFFICIENT: The sum of the exterior angles = 5 Ã— length of each spoke Ã— number of spokes.

360 = 5(8)(x) 360 = 40x 9 = x

The game board has nine sides. The sum of its interior angles is (9 â€“ 2)(180) = 1260.

The correct answer is B.

Got B too but in different way ;

(2) SUFFICIENT: The sum of the exterior angles = 5 Ã— length of each spoke Ã— number of spokes.

360 = 5(8)(x)
how did u get this 360 as sum of the exterior angles; (2) does not say that
unless you deduce it .

In my opinion the answer should be C. We don't know what is the sum of exterior angles. We have to use this information from the first statement,then only we can set up this equation
360=5(8x)
that is sufficient to know the number of sides and hence the sum of interior angles.

Convex polygon is a polygon inwhich each interior angle has a measure of less than 180.

Re: A certain game board is in the shape of a non-convex [#permalink]
27 Apr 2014, 10:42

How can the sum of all exterior angles of a non convex polygon be 360..I take a polygon with n sides and the sides are so acute tat exterior angle is close to 360..Imagine something like the shape of a star just with more side..

_________________

Appreciate the efforts...KUDOS for all

gmatclubot

Re: A certain game board is in the shape of a non-convex
[#permalink]
27 Apr 2014, 10:42