Need help with Algebra problem

[ABQmom]

We are having major difficulties with MUS Algebra I.

 

Here is the problem in question:

 

144 divided by 9 X 3 - the absolute value of 100 - 121 =

 

MUS taught the order of operations as "My Dear Aunt Sally" or Multiplication, Division, addition, and subtraction. If we multiply 9 X 3 first and then divide by 144, we get the wrong answer. Obviously we are missing some important rule here, but I don't know what that is.

[Dana]

That's the danger with that mnemonic.

 

It's multiplication and division in the order they appear from left to right. Then same for addition and subtraction.

[Matryoshka]

We are having major difficulties with MUS Algebra I.

 

Here is the problem in question:

 

144 divided by 9 X 3 - the absolute value of 100 - 121 =

 

MUS taught the order of operations as "My Dear Aunt Sally" or Multiplication, Division, addition, and subtraction. If we multiply 9 X 3 first and then divide by 144, we get the wrong answer. Obviously we are missing some important rule here, but I don't know what that is.

 

How is this written in the book - horizontally like 144 ÷ 9 x 3, or this way

144

9 x 3

 

In order of operations, multiplication/division are equal, as are addition/subtraction. If it's written horizontally, since all operations are an equal level, you'd divide 144 by 9, then multiply the result by 3.

 

If it were written the second way, with 144 as the numerator and 9x3 as the denominator, then you'd multiply first, then divide (or better yet, cancel first).

 

What aren't you understanding in the absolute value question?

 

ETA: Oh - that was another minus sign; I thought it was a hyphen and the absolute value part was a second problem! :tongue_smilie:

Edited November 3, 2010 by matroyshka

[AngieW in Texas]

If it's written the way that you typed it out here, then you would just work the problem from left to right because multiplication and division are the same level and are worked left to right.

 

144 divided by 9 X 3 - the absolute value of 100 - 121 =

144 divided by 9 = 16

16x3 = 48

48-100 = -52

-52 - 121 = -173

[Jenny Piaaree]

When you say "- the absolute value of 100 - 121," do you mean "-|100|-121 or (as I suspect) "-|100-121|"?

 

If it's the first way, it would be

144/9 = 16

16 x 3 =48

48 - 100 = -52

-52 - 121 = -173

 

If it's the second way, it would be

144/9 = 16

16 x 3 = 48

48 - |100-121| = 48 - 21 = 27

 

I hope. It's been a long time... ;)

[Testimony]

We are having major difficulties with MUS Algebra I.

 

Here is the problem in question:

 

144 divided by 9 X 3 - the absolute value of 100 - 121 =

 

MUS taught the order of operations as "My Dear Aunt Sally" or Multiplication, Division, addition, and subtraction. If we multiply 9 X 3 first and then divide by 144, we get the wrong answer. Obviously we are missing some important rule here, but I don't know what that is.

 

I told my son to divide first. I would never multiply first in this problem because 144 totals 9(1+4+4) which means it is divisibly by 9. Thus I would do 144/9=16X3=48

 

Now for those absolute values:

 

48-100=-52-121=-173

 

I think. I'm not 100% on the absolute values.

 

Blessings,

Karen

http://www.homeschoolblogger.com/testimony

Edited November 3, 2010 by Testimony
bad spelling

[Teachin'Mine]

When you say "- the absolute value of 100 - 121," do you mean "-|100|-121 or (as I suspect) "-|100-121|"?

 

If it's the first way, it would be

144/9 = 16

16 x 3 =48

48 - 100 = -52

-52 - 121 = -173

 

If it's the second way, it would be

144/9 = 16

16 x 3 = 48

48 - |100-121| = 48 - 21 = 27

 

I hope. It's been a long time... ;)

 

I get 27 too. I wish there was an easy way to type the math problems because it makes such a difference depending on how the problem is presented. Another thing missing from the MDAS is parentheses - which are always done first. Exponents too. I like "Please excuse my dear Aunt Sally" since it includes these others.

[kiana]

We are having major difficulties with MUS Algebra I.

 

Here is the problem in question:

 

144 divided by 9 X 3 - the absolute value of 100 - 121 =

 

MUS taught the order of operations as "My Dear Aunt Sally" or Multiplication, Division, addition, and subtraction. If we multiply 9 X 3 first and then divide by 144, we get the wrong answer. Obviously we are missing some important rule here, but I don't know what that is.

 

I'm not sure if this is a problem in your phrasing or in concepts. When you say 'divide by 144', do you mean 'divide into 144'? It's important (in math) to clearly say what you mean.

 

I'm guessing that it's 144/9*3, in which case you should divide first and then multiply. For PEMDAS, it really ought to be read as 'Parentheses, Exponents, Multiplication AND Division, Addition AND Subtraction'. This is because multiplication and division really are the same operation -- multiplying by 1/9 is the same as dividing by 9. So we do parentheses and exponents first, then do all the multiplications and divisions, from left to right, in the order in which they occur. Because division is to the left of multiplication, we do it first. The same problem could be written as 144(1/9)(3) in which case the order of operations should be more clear.

[ABQmom]

That's the danger with that mnemonic.

 

It's multiplication and division in the order they appear from left to right. Then same for addition and subtraction.

 

This is what I figured, but couldn't ever remember it being said. Thank you!

 

Sorry for the poorly worded math problem--it's just hard to show it in type when your keyboard doesn't have the right symbols for things. The answer is actually 27. The absolute value lines were around the 100 - 121 meaning to take the absolute value of -21.

 

Thanks so much to everyone for looking at this. Using a mnemonic is okay as long as you know other rules that govern a problem. MUS has always worked out okay for us, but we are really struggling with Algebra I.