Choose numbers that make the arithmetic as easy as possible. Do not plug in numbers that appear in the answer choices or in the question. Do not plug in zero or one. Do not plug in the same number for two different variables. If the question is about money (dollars and cents), choose a multiple of 100. If the question is about time (seconds, minutes, hours), choose a multiple of 60. Even if you love algebra, Plugging In is easier and more foolproof on the GRE.