The midpoint formula was a good piece of info to use further. I went with the approach that if we know both the points then the distance of the line can be calculated and hence the midpoint co-ordinates.

C it is.

IMO:C

This question seems too simple for Answer C.

Is there any hidden GMAT trick

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and equations ensures a solution.


If r and s are positive numbers, what are the coordinates of the
midpoint of line segment MN in the xy-plane?
(1) The coordinates of M are (r; 3 - s).
(2) The coordinates of N are (3 - r; s).

In the original condition there are 2 variables (r,s) thus we need 2 equations to match the number of variables and equations. Since there is 1 each in 1) and 2), C is likely the answer. In actual calculation,

Using both 1) & 2) together, we have ((r+3-r)/2,(3-s+s)/2)=(3/2,3/2) thus the answer is unique. Therefore C is the answer.


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