Simple Equation: 3y + 2 over 4 equals 7Date: 10/17/2001 at 17:11:59 From: Tara Subject: I have some equations I can't seem to understand! 3y + 2 over 4 equals 7 I think you have to subtract 2 on both sides (to get 3y by itself) 3y+2-2 over 4 equals 7-2 3y over 4 equals 5 Now I'm lost! Could you help me out? Date: 10/17/2001 at 22:43:11 From: Doctor Peterson Subject: Re: I have some equations I can't seem to understand! Hi, Tara. You have 3y + 2 ------ = 7 4 Notice what the left side means: you multiply y by 3, then add 2, then divide by 4. When you are undoing these operations, it is necessary to do so in the reverse order. For comparison, suppose I have put on my shirt, then my sweater, then my coat. If I try to take off my sweater before taking off my coat, it will get all tangled up! That's just what happened to you: the addition of 2 is the sweater, and you took it off too soon. It is not true that 3y + 2 3y ------ - 2 = -- 4 4 which is what you are assuming. Actually, we can simplify the left side as 3y + 2 ------ = 3/4 y + 1/2 4 and then subtract 1/2 rather than 2. But if you don't want to simplify, just undo the division (by multiplying by 4) before the addition: 3y + 2 ------ = 7 4 3y + 2 = 7 * 4 3y + 2 = 28 Now you can subtract 2 from both sides, and so on: 3y = 28 - 2 3y = 26 y = 26/3 Does that help? - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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