Crack GMAT Math Problem Solving and Data Sufficiency. Some good tips on solving interesting questions in Number Theory, Permutation Combination, Probability etc.
Thursday, February 23, 2012
Coordinate Geometry DS - Slope of Lines
Here is a data sufficiency question from Coordinate geometry.
Is the slope 'm' of the line y = mx + c positive? 1. The x and y intercepts are both negative. 2. The line passes through the first quadrant.
Correct Answer : Choice A. Statement 1 alone is sufficient.
Positive Sloping Lines : The x and y intercepts of the line are of opposite signs. If the x intercept is positive, the y intercept will be negative. Conversely if the y intercept is positive, the x intercept will be negative.
Negative Sloping Lines : The x and y intercept will be of the same sign. If the x intercept is positive, the y intercept will also be positive. If the x intercept is negative, the y intercept will also be negative.
Statement 1 : x and y intercepts are both negative. The line has to be a negative sloping line. So, we can answer from statement 1 that the line is not positive sloping.
Statement 1 is sufficient. Choice A or Choice D is the answer.
Statement 2: The line passes through the first quadrant. Knowing only one of the quadrants through which a line passes we will not be able to determine whether it is positive sloping. Statement 2 is not sufficient.
As statement 1 alone is sufficient, while statement 2 is not choice A is the correct answer.