Advanced Error Log: Tie Your Hands Behind Your Back

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Manhattan Prep GMAT Blog - Advanced Error Log: Tie Your Hands Behind Your Back by Reed Arnold

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It’s been said that “a mistake is only a mistake if you don’t learn from it,” which probably explains the shambles of my dating life.

Hopefully by now you’ve created an error log and have been redoing problems you need to redo. This is crucial to your improvement on the GMAT. I’m a little tired of students coming in for a session and saying, “I’ve done every problem in every book I can find, but I’m not scoring better on practice tests! Why?” Because doing a problem isn’t learning from a problem. You have to do it, review it thoroughly, and then come back to that problem. More than once. Your memory needs a chance for the concept you’re learning from that problem to stick.

For such things, we’ve advocated that you keep an error log for problems you need to redo. When my students miss a question, or get it right but it takes a while, or get it right but it was a little lucky or didn’t feel ‘smooth,’ I tell them to log it into an error log and redo it on a set schedule: in 2-5 days, then a week after that, then 2 weeks after that, then 3 weeks after that, etc. This gives more and more space between their re-dos so that a long-term memory can form. If at any point they get the question right or they can’t remember why the answer is what it is or how to get there, I tell them to go back to 2-5 days and start over.

There’s a new trick I’ve thought about, though, that might make the error log even more useful. Let’s say you get a question right, in time, and smoothly the first time you come to it. Are you done with it forever? Perhaps. But you should still review it. See if there’s another way. See if there’s a way you could have guessed. Maybe you could have backsolved? It might have been slower on this particular problem relative to the way you solved, but you should still be able to backsolve for the test—are you able to do it here? If not, you might want to put this into your error log with an additional note for your redo: “must backsolve.” Or tell yourself that you can’t use whatever method you had used. That is, tie your hands behind your back on the problem (I call it the ‘Fifty Shades of Grey’ approach).

Prevent yourself from using the method you found easiest.

Why? Because it’s entirely possible that for some other problem, your first method won’t work or will be especially daunting, but the alternative method will be useful, so you’ll need that alternative method. For instance, I know several ways to do weighted average problems. For most questions, I know that one particular method works perfectly, but I once came to a question on which the numbers the GMAT gave made that method an arithmetic nightmare. However, one of my other approaches—one I use less often—made the math downright easy. I wouldn’t have been able to use that method had I not practiced it on other problems when I didn’t really need to use it.

So let’s say I do an SC question, and I eliminate every answer choice but one really quickly, because there’s an opening modifier problem and only one answer modifies correctly. Great, but I should now ask myself, “what if this particular split wasn’t there?” I go on a hunt, and after a bit of time (and a review of the explanation), I find that two answers can be eliminated using parallelism and the others have a subtle verb tense issue. This is an opportunity to learn, so I shouldn’t waste it. On my error log, I specify to myself, “must ignore the opening modifier errors.” This will help me improve recognition of these other mistakes I’m not as keyed into noticing so I can more quickly find them on other questions.

Or say you have this Quant question:

The chickens on Tom’s farm increased by 20% every year for 5 years and at the end of 5 years he had 7,776 chickens. How many chickens did he start with?

You solve it using a perfectly nice algebra equation (it’s not perfectly nice, but well done). And then you review this question and someone on our forums points out, “If I’m increasing by 20% and I both start and end with integers, my original number must be a multiple of 5.” You might think, “What? Why? How did he know that?” so you wrestle with it until you understand. But then you note, “Two of the answers are multiples of 5, though, so this trick only helps me get to 50-50.” Well, your algebraic approach is probably better for this question. However, this is a nifty number property that might serve you in other questions. So you can put it in your error log with the instruction, “Cannot set up equation.”

When you do this, don’t let yourself forget the best way to work through these problems. Remind yourself what that is, and practice it occasionally to stay sharp. But if you want to milk a little bit of extra knowledge from your problems, you can force yourself to do them a different way. In the end, you’ll broaden your understanding of the methods available on the GMAT, you’ll be prepared to mix up strategies or to make an educated guess, and you’ll become a better test-taker. 📝


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Reed Arnold is a Manhattan Prep instructor based in New York, NY. He has a B.A. in economics, philosophy, and mathematics and an M.S. in commerce, both from the University of Virginia. He enjoys writing, acting, Chipotle burritos, and teaching the GMAT. Check out Reed’s upcoming GMAT courses here.

  1. Rahul Sehgal August 28, 2017 at 1:50 pm

    A great article.