vscid wrote:

ABCD has an area equal to 28. BC is parallel to AD. BA is perpendicular to AD. IF BC is 6 and AD is 8, then what is CD?

1] 2√ 2

2] 2√ 3

3] 4

4] 2√ 5

5] 6

28 = (ab x bc) + (1/2) (ab) (ad-bc)

28 = 6ab + (1/2) (ab) (8-6)

28 = 6ab + ab

28 = 7ab

ab = 4

(cd)^2 = (ab)^2 + (ad-bc)^2

(cd)^2 = (4)^2 + (8-6)^2

(cd)^2 = 16 + 4

(cd)^2 = 20

cd = 2√5

so D. (updated for typo).

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Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html

Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

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