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Trapezoid DS

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by knight247 » Sat Feb 11, 2012 4:19 am
A trapezoid is symmetrical about a vertical center line. If a circle is drawn such that it is tangent to exactly three sides of the trapezoid and is enclosed entirely within the trapezoid, what is the diameter of the circle?
(1)The parallel sides of the trapezoid are 10 inches apart.
(2)Of the parallel sides of the trapezoid, the shorter side is 15 inches long.

OA is C
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Source: — Data Sufficiency |

by GMATGuruNY » Sat Feb 11, 2012 6:08 am
knight247 wrote:A trapezoid is symmetrical about a vertical center line. If a circle is drawn such that it is tangent to exactly three sides of the trapezoid and is enclosed entirely within the trapezoid, what is the diameter of the circle?
(1)The parallel sides of the trapezoid are 10 inches apart.
(2)Of the parallel sides of the trapezoid, the shorter side is 15 inches long.

OA is C
DRAW.

Statement 1: height = 10.
Different diameters are possible:
Image
INSUFFICIENT.

Statement 2: shorter base = 15.
Different diameters are possible:
Image

Statements 1 and 2 combined: height = 10, shorter base = 15.
Since the height is less than the shorter base, the following won't work:
Image

Since the circle must be fully inside the trapezoid, only d=10 is possible:
Image

The correct answer is C.
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by [email protected] » Wed Feb 15, 2012 4:30 am
thanks gmatguru and knight 247 for a wonderful question...
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