Why keep a GMAT error log?
What usually happens when you encounter a difficult GMAT math problem for a second time that you struggled to solve initially? Do you cruise right through the solution? Or do you hem and haw and spin around in the same frustrating circles you did the first time you saw the problem? If the latter, it’s time to ask yourself a serious question: if you can’t even solve difficult problems that you’ve already seen, what chance do you have of solving the difficult problems you’ll see for the first time when you take the real GMAT? If you’re not retaining the things that you learn when you do practice problems, you’re wasting your time.
Retaining a newly learned mathematical concept is a bit like trying to keep a non-helium balloon up in the air: you have to keep tapping it to keep it afloat. If you only tap it once and then forget about it for weeks, don’t be shocked when you come back and discover that it’s on the ground. As a private tutor, the most frustrating thing that I experience (professionally) is when I’m able to successfully help a student really understand a new concept, and then a week later he or she has totally forgotten how to use it. Remember that the only thing that a tutor or GMAT book or a generous guy on a forum can do is help you get that balloon off the ground. After that it’s entirely on you to keep it afloat. And I don’t know of any better way to do that than by keeping a detailed error log and reviewing it constantly.
So what should go in your error log? Each entry should include the following things: the problem, the nature of your error or difficulty, what you tried the first time and why it worked or didn’t work, a complete solution, and any points you want to take away from the problem. An entry might look something like this:
The good news is that very few math problems are unique. Any concept that you learn from any specific GMAT problem will most likely be applicable to some other problem. But first you have to understand the concept well and retain it. If you review the above entry in your error log two or three times per week, your chances of forgetting any of the key concepts will be very low. What’s more, you’ll be more likely to think of using them if you encounter a similar problem.