Apr 1, 2008 at 11:57 PM Thread Starter

#### cantsleep

very simple. 2+2x2=6, not 8
the rule states that we do multiplication/division before addition/subtraction. but why?

Apr 2, 2008 at 12:01 AM

#### Wodgy

Because it's a convention to avoid fully parenthesizing expressions. Nothing more. The convention could be anything you like.

If this bugs you, get a Reverse Polish Notation (RPN) calculator and control the order of operations yourself.

Apr 2, 2008 at 12:04 AM

#### pez

Well usually when you see a problem like this it is divided by parenthesis. I'm sure you are familar with PEMDAS or as some refer to as Please Excuse My Dear Aunt Sally. Since these are usually placed inside parenthesis, and the rule states that you do the parenthesis first, you would have to what's inside them first, which in this case is (2x2). After that is solved, the parenthesis are negated and you can then find the final solution.

Apr 2, 2008 at 12:09 AM

#### Duggeh

##### Indeed
PEMDAS? I was taught BODMAS (brackets, order, division, multiplication, addition, subtraction). Whats PEMDAS? (parenthesis, exponentials, multiply, divide, add, subtract)?

Apr 2, 2008 at 12:14 AM

#### Mher6

Quote:

 Originally Posted by Duggeh /img/forum/go_quote.gif PEMDAS? I was taught BODMAS (brackets, order, division, multiplication, addition, subtraction). Whats PEMDAS? (parenthesis, exponentials, multiply, divide, add, subtract)?

Yep, that's what PEMDAS is and that's the way I was taught.

Apr 2, 2008 at 12:45 AM

#### DNT

So PEMDAS and BODMAS are two different systems? One says division first and the other says multiplication. So which one is conventionally correct?

Apr 2, 2008 at 12:56 AM

#### Febs

Multiplication is cummutative. In other words, the order may be changed without changing the result.

Division is the same as multiplication by a reciprocal.

X/Y = X * 1/Y

Thus, the order does not matter.

Apr 2, 2008 at 12:56 AM

#### The Actual

^division is multiplication by a reciprocal. Either system is left to right with division/multiplication.

(x*y)/z=x*(y/z)=x*y/z

EDIT: I agree, Febs.

Apr 2, 2008 at 12:59 AM

#### shellylh

##### Sugar and spice and all things nice
Quote:

 Originally Posted by Wodgy /img/forum/go_quote.gif Because it's a convention to avoid fully parenthesizing expressions. Nothing more. The convention could be anything you like. If this bugs you, get a Reverse Polish Notation (RPN) calculator and control the order of operations yourself.

x2, well said

Apr 2, 2008 at 1:04 AM

#### Arainach

It's not a Linear Order, it's a Heirarchy. The standard system goes something like (top is highest priority):

Parenthesis
Negation (the unary - operator)
Exponentiation/Roots
Multiplication/Division

And, if one gets into programming, below this comes the bitwise shifting operations, than the comparative operators, than the bitwise logical operators, than the various logical operators.

Apr 2, 2008 at 1:14 AM

#### FallenAngel

PEMDAS, BODMAS, meh, in Ukraine we were taught to remember the order of operations with a ruler across the hands. It's effective and you remember damn well.

Apr 2, 2008 at 1:26 AM

#### Born2bwire

##### 25+ Member ;-)
Because we're forward thinking Americans, not like those silly Polish.

Apr 2, 2008 at 1:31 AM

#### goldenratiophi

Quote:

 Originally Posted by Arainach /img/forum/go_quote.gif Parenthesis Negation (the unary - operator) Exponentiation/Roots Multiplication/Division Addition/Subtraction

huh? Negation is just multiplication by -1. If negation is to be read first then you'd have -5^2 = 25. However we write -5^2 = -25 and (-5)^2 = 25. Unless I'm misinterpreting what you mean by negation...

Apr 2, 2008 at 1:37 AM