Solving an Equation with DecimalsDate: 1/31/96 at 19:57:19 From: Anonymous Subject: Algebric Equations I can't figure out what 15.6 + z = 20.4 is. I need step by step help. Date: 2/2/96 at 10:40:11 From: Doctor Elise Subject: Re: Algebric Equations The way you solve any algebra problem is by putting all the letters on one side of the equals sign, and all the numbers on the other. The rule is that you can do anything you want to the equation as long as you do the same thing on both sides of the equals sign. Okay. 15.6 + z = 20.4 What we need to do is get the equation to look like "z = something". So we need to subtract the 15.6 from the left side of the equals sign. We have to do the same thing to both sides, so what we'll do is this: 15.6 + z - 15.6 = 20.4 - 15.6 From the very beginning of math, you learn that 2 + 3 = 3 + 2, our old friend the "commutative property" of addition. What this really means is that if you have to add and subtract numbers (and letters) you can rearrange them in any order and it doesn't make any difference. In fact, rearranging the order is about the ONLY thing you don't have to do to both sides of the equals sign. So I can write: 15.6 - 15.6 + z = 20.4 - 15.6 Now, 15.6 - 15.6 is 0, so now I have: 0 + z = 20.4 - 15.6 I know that 0 + z is equal to z, so I'll get rid of the 0 and get z = 20.4 - 15.6 And then you can go ahead and do the 20.4 - 15.6 part. Be sure to estimate first so that you know what your answer should be: after all, this is "a little more than 20 minus a little more than 15", so the answer should be pretty close to 5. Good luck! -Doctor Elise, The Math Forum |
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