gmatpre - xy plane

[Gurpinder]

[Ian Stewart]

We certainly need information about both lines to answer the question, so neither statement could be sufficient alone.

From statement 1, we know two points on line L - we know (0,0) and (1,2) are on the line. From two points, we can find a slope. From statement 2, we know two points on line K - we know (4, 0) and (0,2) are on the line. Again, from two points we can find a slope. Since using both statements, we can find the slopes of L and K, we could certainly determine if the product of these slopes is -1 and thus answer the question. So the answer is C.

Notice that we don't actually need to do any calculations here, since it's Data Sufficiency; we only need to know if it will be possible to answer the question.