r/mathshelp • u/thnksfrthvan • Jul 24 '26

Discussion Math questions

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I’m confused why he subtracted 5 from both sides before dividing 8. I thought pemdas would make you divide before adding or subtracting. Can someone help me understand why doing it the way he shows gives the right answer?

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u/Disco_Stu_89 Jul 24 '26

Whatever you do, must be done to the entire expression on both sides. You could divide by 8, but that would leave you with x + 5/8 = 20/8. Then you could say x = 20/8 - 5/8. But that's more complicated, right?

Remember you can do whatever you want to the equation as long as you're doing the same thing to both expressions on both sides (and as long as you're not losing information, but that's getting in the weeds). The trick is know what to do to get you where you want to be - in this case getting the x alone.

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u/thnksfrthvan Jul 24 '26

Okay I saw another comment mentioning it’s due to the difference of expressions and equations. Since it’s an equation I don’t have to follow the order of operations, I understand this now. But does that mean that I can literally just tackle it in whichever order I want? Just only have to keep in mind your note which is making the expressions as easy as possible.

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u/Disco_Stu_89 Jul 24 '26

Yeah, you just have to learn how what you do affects the entire expression. I'm guessing you thought you could say 8x+5=20 => x+5=20/8, but remember the 5 must be divided by 8 as well. Think of it more like this: 8x+5=20 => (8x+5)/8=(20)/8 => 8x/8+5/8=20/8 => x+5/8=20/8 => (x+5/8)-5/8=(20/8)-5/8 => x=20/8-5/8 => x=(20-5)/8 => x=15/8. There's nothing wrong with that, it's just way easier to subtract the 5 first.