Checking Your Work
Date: 9/9/96 at 22:1:45 From: Anonymous Subject: Little (stupid) mistakes Dr. Math, I've had problems keeping myself from doing little mistakes such as not putting commas in, putting the decimal point in the wrong place, and writing down the wrong number (though I HAVE gotten better about that!). I've tried to check over everything, but I still end up making those mistakes (I have to admit, I DO do better if I check over everything)! How can I stop doing this? Jennifer
Date: 9/10/96 at 19:56:40 From: Doctor Tom Subject: Re: Little (stupid) mistakes Hi Jennifer, There are a few things you can do: 1) Check your answer by plugging it back into the equations or into the problem to see if it works. For example, if you're solving for x in: 5x - 3 = 17, and you get x = 5, try it out: 5*5 - 3 = 17? 25-3 = 17? 22=17? Nope! 2) This method works better for word problems than equations, and that's to try to get a feeling for what the answer should be before you work it out (at least roughly). Then see if the answer you get is out of the ballpark. For example, suppose you're talking about a trip to the store, and you buy items costing $1.76, $2.43, $5.01, $11.43, ... about 10 items like that. What's the total cost? Take a look at all the numbers. In this case, it looks like the rough "average" (just by eye-balling them) is about 5 bucks each. So an answer of about $50 is roughly right. If you get $500 or $5, you know you're out of the ballpark. 3) If you can figure out how to do a problem in more than one way, this is the best solution of all. Your answers had better agree. Even for simple problems like addition you can do this. For example, when I'm adding up the numbers in my checkbook, if I really care about the answer, I'll do it twice, but once I'll start typing them into the calculator from the top of the list to the bottom, and the next time, I'll type them in from bottom to top. If I do it the same way both times, I'm much more likely to make the same mistake both times. I hope this helps some. -Doctor Tom, The Math Forum Check out our web site! http://mathforum.org/dr.math/
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