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Is area of triangle ABC greater than area of triangle DEF?

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by conquistador » Mon Oct 12, 2015 2:45 pm
Source: Gmatclub

Is area of triangle ABC greater than area of triangle DEF?

(1) The value of area of ABC is less than that of perimeter of DEF.
(2) Angles of ABC = Angles of DEF

OA E
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Source: — Problem Solving |

by ceilidh.erickson » Tue Oct 13, 2015 2:55 pm
The wording on this question is a little bit strange - we shouldn't be able to directly compare a 2-dimensional area to a 1-dimensional perimeter. But - here's the logic behind this question....

Target question: is the area of ABC > area of DEF?

(1) The value of area of ABC is less than that of perimeter of DEF.


Here, test different values to try to prove insufficiency.

Scenario 1: ABC is an isosceles right triangle with a base of 1 and a height of 1, thus an area of 1/2. DEF is an isosceles right triangle of base 10 and height 10, thus an area of 50 and a perimeter of 20 + 10(sqrt2). DEF has both the greater perimeter and the greater area, so the answer is NO.

Scenario 2: ABC is an isosceles right triangle with a base of 2 and a height of 2, thus an area of 2. DEF is an isosceles right triangle of base 1 and height 1, thus an area of 1/2 and a perimeter of 2 + (sqrt2). DEF has the greater perimeter, but ABC has the greater area, so the answer is YES.

Insufficient.

(2) Angles of ABC = Angles of DEF

If all angles are the same, the triangles are similar, but that doesn't tell us anything about scale. Insufficient.

(1) & (2) Together:

In the examples we used in statement 1, all of the triangles were 45-45-90, but that did not allow us to compare area to perimeter. Insufficient.

The answer is E.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
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