gmat prep

[girishbtg]

...

[GMATGuruNY]

When we want to see how the angles in a figure affect each other, we can use the following strategy:

Plug in twice, following the rules of geometry.

Why twice? So we can see what happens to the value of PRS-PQR.

If the value of PRS-PQR stays the same, the statement is sufficient.
If the value of PRS-PQR changes, the statement is insufficient.

As we plug in, we have to follow the rules of geometry. If angles are inside a triangle, their sum must be 180. If angles form a straight line, their sum must be 180.

The attached .pdf shows two combinations of angle measurements that satisfy both statements 1 and 2. In each case, PRS-PQR=30. Since the value of PRS-PQR stays the same, each statement is sufficient.

The correct answer is D.

The advantage of this approach is that no special insight is needed. To answer the question correctly, all we have to do is follow the rules of geometry. Plugging in can make a seemingly hard geometry question much, much easier.