GRE Sample Test 1 Quantitative Reasoning 1

Because ΔQRS is isosceles, side RS must be equal to one of the other sides, and x could measure 4 or 7. Thus, the perimeter could be 4 + 4 + 7 = 15, or the perimeter could be 4 + 7 + 7 = 18. You can’t tell if the perimeter is greater or less than 17, so the answer is (D).
Remember, you cannot trust the figure to be drawn to scale!