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In this video we are gonna talk a little bit
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about order of operations.
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And I want you to pay close attention
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because, really, EVERYTHING else that
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you are gonna do in mathematics is going to be based on
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your having a solid grounding in Order of Operations.
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So, what are we even talk...mean,
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when we say Order of Operations?
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So let me give you an example.
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The whole point, is so we have one way
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to interpret a mathematical statment.
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So let‘s say I have the mathematical statement:
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7 plus 3, times 5.
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Now if we didn't all agree on Order of Operations,
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there would be 2 ways of interpreting this statement.
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You could just read it left-to-right.
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So you could say "well, let me just take 7 + 3."
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You could say 7 + 3 and then multiply that times 5 -
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and 7+3 is 10.
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and then you multiply that by 5.
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10 x 5, it would get you 50.
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So, that's one way you would interpret it
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if we didn't agree on an order of operations -
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maybe it's a natural way - you just go left-to-right.
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Another way you could interpret it -- you say
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"oh, I like to do multiplication before I do addition"
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so you might interpret it as - I'll try to color code it -
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7+ ... and you do the 3x5 first
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7 + 3x5 which would be 7+
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3x5 is 15 ... and 7+15 is 22.
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So notice we interpreted this statement in two different ways
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this was just straight left-to-right,
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doing the addition, then the multiplication.
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This way, we did the multiplication first,
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then the addition. We get 2 different answers.
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That's just not cool in mathematics.
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If this was part of some effort to send something to the Moon
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because 2 people interpreted it a different way
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or 1 computer interpreted it one way
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and another computer interpreted it another way -
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the satellite might go to Mars!
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So this is just completely unacceptable,
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and that's why we have to have
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an agreed upon Order of Operations.
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an agreed upon way to interpret this statement.
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So, the agreed upon order of operations
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is to do parentheses first.
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-- let me write it over here --
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'parentheses' first. then do exponents.
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If you don't know what exponents are,
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don't worry about it right now. In this video
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we're not going to have exponents in our examples.
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So you don't really have to worry about it for this video.
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Then you do multiplication -
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I'll just write "mult" short for multiplication.
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Then you do multiplication and division next.
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they kind of have the same level of priority.
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And then finally you do addition and subtraction.
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So, what is this order of operations?
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Let me label it - this right here is,
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that is the agreed upon order of operations
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and if we follow these order of operations
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we should always get to the same answer
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for a given statement. So what does this tell us?
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What is the best way to interpret this up here?
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Well, we have no parentheses -
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parentheses look like that,
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these little curly things around numbers.
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We don't have any parentheses here -
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I'll do some examples that do have parentheses.
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We don't have any exponents here,
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but we do have some multiplication and division
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or we actually just have some multiplication.
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So the order of operations say
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'do the multiplication and division first'.
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So it says do the multiplication first -
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that's a multiplication. So it says do this operation first.
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It gets priority over addition or subtraction.
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So if we do this first, we get the three times five,
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which is fifteen, and then we add the seven.
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The addition or subtraction - I'll do it here
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we just have addition - just like that.
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So we do the multiplication first, get 15,
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then add the 7 ... 22
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So based upon the agreed order of operations,
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this right here is the correct answer -
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the correct way to interpret this statement.
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Let's do another example.
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I think it'll make things a little bit more clear.
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And I'll do the example in pink.
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So let's say I have 7+3
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- put some parentheses there -
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x 4 divided by 2 - 5 x 6.
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So there's all sorts of crazy things here,
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but if you just follow the Order of Operations,
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you'll simplify it in a very clean way
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and hopefully we'll all get the same answer.
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So let's just follow the order of operations.
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The first thing we have to do is look for parentheses.
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Are there parentheses here? Yes, there are!
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There's parentheses around the 7+3.
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So it says, "lets do that first". So 7+3 is 10.
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So this we can simplify
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- just looking at this order of operations -
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to 10 times all of that. Let me copy and paste that,
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so I don't have to keep rewriting it.
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So, let me copy. Let me paste it.
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So that simplifies to ten times all of that -
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we did our parentheses first. Then what do we do?
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There are no more parentheses in this expression.
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Then we should do exponents.
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I don't see any exponents here.
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and just so if you are curious what exponents would look like
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an exponent would look like
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- you know, seven squared -
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You'd see these little small numbers up in the top right.
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We don't have any exponents here,
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so we don't have to worry about it.
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Then it says to do multiplication and division next.
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So where do we see multiplication -
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we have a multiplication, a division, a multiplication again.
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Now, when you have multiple operations at the same level
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and in our order of operations, multiplication and division
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are at the same level - then you do left-to-right.
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So in this situation, you're going to multiply by 4
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and then divide by 2. You won't multiply by 4 divided by 2.
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Then we'll do the 5 times 6 before we do the subtraction,
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right here. So let's figure out what this is.
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So we'll do this multiplication first.
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We'll do that multiplication first -
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we could simultaneously do this multiplication
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cause it's not going to change things,
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but I'll do things one step at a time.
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So the next step we're going to do is this 10x4.
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10x4 is 40
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Then you have 40 divided by 2
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- let me copy and paste all of that again -
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Then it simplifies to that right there.
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Remember multiplication and division,
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they are at the exact same level -
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so we're going to do it left-to-right.
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You xould also express this as multiplying by one-half
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and then it wouldn't matter the order. But for simplicity
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multiplication / division go left-to-right.
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So then you have 40 divided by 2 minus 5 times 6.
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So, division - you just have 1 division here -
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You want to do that. This is going to take...
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You have this division and this multiplication.
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They are not together.
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So you can actually kind of do them simultaneously.
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And to make it clear that you do this before you do the subtraction,
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because multiplication/division take priority over addition/subtraction
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we can put parentheses around them.
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Just say "look, we're gonna do that and that first,
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BEFORE I do that subtraction"
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because multiplication / division have priority.
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So 40 divided by 2 is 20.
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We're going to have that minus sign.
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-5 times 6 is 30.
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20 minus 30 is equal to negative 10.
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And that is the correct interpretation of that.
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So I want to make something very, very, very clear:
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if you have things at the same level
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so if you have 1 + 2 - 3 + 4 - 1
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so addition and subtraction are at the same level
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in order of operations - you should go left-to-right.
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You should interpret this as 1+2 is 3.
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So this is the same thing as 3 - 3 + 4 - 1.
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Then you do 3 - 3 is 0, + 4, - 1.
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OR this is the same thing as 4 - 1
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which is the same thing as 3 - you just go left to right.
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Same thing if you have multiplication and division
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all on the same level.
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So if you have 4x2, divided by 3, times 2,
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you do 4x2 is 8, divided by 3, times 2
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and you say 8 divided by 3 is - well you get a fraction there -
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it would be 8/3. So this would be 8/3 times 2.
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And 8/3 times 2 is equal to 16/3.
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THAT's how you interpret it - you don't do this multiplication first,
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and then divide the 2 by that, and all of that.
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Now the one time you can be loosey-goosey with order of operations
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is if you have ALL addition or ALL multiplication.
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So if you have 1+5+7+3+2
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does not matter what order you do it in.
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You could do the two plus three;
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you could go from the right to the left;
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you could go from the left to the right;
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you could start some place in between -
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if it's ONLY all addition -
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and the same thing is true if you have ALL mutliplication -
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if it's 1 times 5 , times 7, times 3, times 2
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does not matter what order you are doing it in.
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That's only with all multiplication OR all addition.
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If there's some division in here or some subtraction in here,
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you're best off just going left-to-right.