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by GMATGuruNY » Fri Jan 02, 2015 1:12 am
The points A, B, C, and D are on a number line, not necessarily in that order. If the distance between A and B is 18 and the distance between C and D is 8, what is the distance between B and D?

(1) The distance between C and A is the same as the distance between C and B.

(2) A is to the left of D on the number line.
The drawings below satisfy both statements:
Image
Since in the first case BD=1 and in the second case BD=17, the two statements combined are insufficient.

The correct answer is E.
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by ceilidh.erickson » Sat Jan 03, 2015 5:53 pm
To add to Mitch's explanation...

When number lines are discussed on the GMAT, they are often testing properties of absolute value - in other words, we must think of both positive and negative cases. You cannot simply subtract to get a difference. It's best to draw the number line as Mitch did, and draw both the positive and negative possibilities for each statement.
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