robu
In the xy–coordinate plane, a line segment is drawn to join the points A (2, 1) and C(4, 3). If point B lies on line segment AC, is AB = BC?
(1) The x-coordinate of point B is 3
(2) The y-coordinate of point B is 2
Dear
robu,
I'm happy to respond.

I'm curious about the source. This feels not so much like a real GMAT question, but more like a review question from a review book about introductory coordinate geometry problems. This is about seven notches easier than an actual GMAT question.
Once a line is specified, then obviously specifying either the x- or y-coordinate of the point will specify the exact point on the line, which will full establish whether the point is the midpoint.
Also, here's a diagram. The fact that this line has a slope of one and involves three consecutive lattice points is further evidence of how simplistic this question is:
Attachment:
midpoint diagram.JPG [ 18.05 KiB | Viewed 4874 times ]
Everything is significant. Answer = (D).
For coordinate geometry questions that are significantly more test-like, see:
Challenging Coordinate Geometry Practice QuestionsMike
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Mike McGarry
Magoosh Test PrepEducation is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)