Serious problems understanding which things to do first

[Amaz1ng]

Ugh...I am trying to review all the fundamental things in algebra because I have calculus, linear algebra, and a comp science curriculum coming up. I've never been one that "just gets" math but I like it and I don't think there's anything really hard about it.

But there's one thing that's getting on my nerves...I bought a book for myself that has a ton of problems. Every time I do a problem, I don't do the operations in the correct order and therefore it's wrong. For example, I can come up with my solution and check the back of the book only to see my answer incorrect. But I can instantly see how the author got his answer by reworking it again.

How do I know the correct order of the operations to do. Someone told me to use SADMEP (PEMDAS reversed) but it doesn't seem to work. ;o

And this is basic algebra...

 

[Pengwuino]

I assume you have an algebra text with you that you are using to practice right? If so, just check out the section on order of operation and use the practice problems there.

 

[Amaz1ng]

So you just use the order of operations? parenthesis, then exponents, then multiply, etc?

 

[Pengwuino]

So you just use the order of operations? parenthesis, then exponents, then multiply, etc?

Yes that's one part of the foundation you need in order to advance beyond algebra. Consider everything a little sub-problem. Let's assume you're given a problem and you're told what the value of 'x' is. If you have something like

$${{\left(5x*2^{9x-5} - 9\right)} \over {3x-3}}$$

you would compute things in parenthesis first. So you'd either want to pick the numerator or the denominator's equation in parenthesis. Say you pick the numerator as it's own sub-problem, then you look for more parenthesis, but there are none. So then your next operation for that sub-problem is exponents, which there is one. That becomes it's own sub-problem and now you start your order of operations again on the 9x-5 part. Is there parenthesis? No. Exponents? No. Multiplication? Yes! The 9x. Then there's the subtraction, which is last.

So you have that sub-problem figured out (let's assume you are given 'x' so it's a matter of just plugging in numbers). Whatever that comes out to be, you can then determine whatever $$2^{9x-5}$$ is. At that point you've come down a level and you're only doing with the numerator. Again, no parenthesis, you've already computed the exponent (that is, $$2^{9x-5}$$) , now you need to go through the multiplication/division. That's simple enough because there is only the 5x multiplying the exponent. Finally, the last operation, addition/subtraction, tells you to subtract 9 from that part.

After that, you look a the denominator as it's own sub-problem and go through the list again. Parenthesis? No. Exponents? No. Multiplication? Yes! Just the 9x. Then finally, whatever that is, subtract 5 from it as your last operation.

Finally look at the whole problem, you know the numerator, you know the denominator. You can then divide and figure out what everything is.

 

[AlexChandler]

I think that all of us can really only tell you what the book is going to tell you. My advice is just to simply practice a LOT. Order of operations is just a notation convention that we all follow in order to avoid confusion.
If you are still having trouble after a lot of practice, visit the website KhanAcademy.org
If anybody can explain things best, it is Khan. He has a collection of wonderful videos ranging from 1+1 to linear algebra and differential equations. Of course it is all free. He has designed exercises that follow the videos. If you are having trouble with an exercise, there is a link to the corresponding video right on the page.
Give it a try, I think you will find it much more helpful than working out of a textbook.

 

[Amaz1ng]

I think that all of us can really only tell you what the book is going to tell you. My advice is just to simply practice a LOT. Order of operations is just a notation convention that we all follow in order to avoid confusion.
If you are still having trouble after a lot of practice, visit the website KhanAcademy.org
If anybody can explain things best, it is Khan. He has a collection of wonderful videos ranging from 1+1 to linear algebra and differential equations. Of course it is all free. He has designed exercises that follow the videos. If you are having trouble with an exercise, there is a link to the corresponding video right on the page.
Give it a try, I think you will find it much more helpful than working out of a textbook.

I got a month sub to mathway.com. That site is pretty neat in that it shows you the steps which has been extremely helpful. It's getting very easy to solve these little algebra probs now. =D