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GMAT Prep: Geometry

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by erdnah » Mon Aug 27, 2007 11:04 am
If a and b are both positive numbers, what are the coordinates of the midpoint of the line segment CD in the xy-plane?

(1) The coordinates of C are (a, 1-b).
(2) The coordinates of D are (1-a, b).
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Source: — Data Sufficiency |
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by radhika1306 » Mon Aug 27, 2007 11:37 am
C
Both statements are needed
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by erdnah » Mon Aug 27, 2007 11:58 am
can you explain?
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by Bharat » Mon Aug 27, 2007 11:32 pm
For obtaining midpoint coordinates of a line segment, you need to take average of x & y coordinates of the endpoints respectively.

Using any one piece of information, you can't solve (because the other end is unknown); however, if you use both the pieces together, the answer is:
x-coordinate = (a + (1-a))/2 = 1/2 [i.e. average of x coordinates of both ends]
y-coordinate = (b + (1-b))/2 = 1/2 [i.e. average of y coordinates of both ends]
=> Midpoint is (1/2, 1/2)
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by erdnah » Tue Aug 28, 2007 1:35 am
thanks a lot @bharat! :D
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by Bharat » Fri Aug 31, 2007 1:21 am
You are welcome Erdnah!! :)
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