Tips for Answering GMAT Problem Solving Questions
Following are some GMAT tips that apply specifically to Problem Solving questions — one of the two basic question formats you'll encounter during the exam's Quantitative section. (Also see this tutorial, which expounds on some of these tips.)
Start with a "ballpark" estimate. Where a problem's solution is a specific numerical value, first try to roughly estimate the size of the number the question asks for. If you come up with a solution that's far off the mark, your ballpark estimate can serve as an alert. A good estimate can also help you eliminate outliers among the wrong answer choices.
Take the shortest route to the answer. Always look for a shortcut to crunching numbers — a more intuitive way of determining the correct answer. Many Problem Solving questions are designed so that you can find the solution by taking either a long way or a shorter, more efficient way. So if you find yourself doing a lot of pencil work, there's probably an easier way.
Don't rely on visual measurements. In a problem based on a geometry figure, the figure will be drawn proportionately unless it is accompanied by a note indicating that it is not drawn to scale. But in any event, don't rely on your eye to measure angle sizes, line segment lengths, or areas. Instead, solve the problem using the numbers provided and your knowledge of mathematics. The test makers are careful to ensure that no problem can be solved merely by visual measurement or estimation.
Try reverse-engineering the answer. You might be able to solve some problems by working backwards from the answer choices to the problem — in other words, by assuming hypothetically that each answer choice in turn is the correct one and then testing it by "plugging it in."
Use pencil and paper for all but the simplest calculations. And double-check those calculations before confirming your response. Keep in mind that incorrect answer choices often anticipate commonly made computational errors — for example, using addition where subtraction would be correct.
Don't split hairs in analyzing story problems. Make reasonable real-world assumptions when handling so-called "story" problems (math problems cast in a real-world setting). Don't split hairs by looking for subtle meanings or ambiguous language. The GMAT is not designed to trick you in this way.