Bokons Posted February 19, 2009 Share Posted February 19, 2009 Ds10 is using CLE math 4, and just started 408. The first lesson was order of operations (although CLE calls it a little differently). I am confused about whether to always do multiplication before division, or only when it comes before division when going left to right. For example, 12-10/5+4x5 (I had to use / for the division sign since my computer doesn't have it). Would we do the 4x5 first, or the 10/5 since it comes before the multiplication when going from left to right? I have the same question about addition and subtraction, eg. 12-2+20. Would we do the 12-2 first, or the 2+20? Thanks for any help. Quote Link to comment Share on other sites More sharing options...
AnnetteB Posted February 19, 2009 Share Posted February 19, 2009 (edited) I do believe that it is all multiplication and division as you come to them from left to right. There are websites that describe the order. The mnemonic: "Please Excuse My Dear Aunt Sally" works, too. Parentheses, Exponents, Multiplication or Division, Addition or Subtraction working left to right. http://www.mathgoodies.com/lessons/vol7/order_operations Maybe this will be helpful. :) Edited February 19, 2009 by AnnetteB Quote Link to comment Share on other sites More sharing options...
mamaof2andtwins Posted February 19, 2009 Share Posted February 19, 2009 Ds10 is using CLE math 4, and just started 408. The first lesson was order of operations (although CLE calls it a little differently). I am confused about whether to always do multiplication before division, or only when it comes before division when going left to right. For example, 12-10/5+4x5 (I had to use / for the division sign since my computer doesn't have it). Would we do the 4x5 first, or the 10/5 since it comes before the multiplication when going from left to right? I have the same question about addition and subtraction, eg. 12-2+20. Would we do the 12-2 first, or the 2+20? Thanks for any help. When simplifying you do multiplication and division in order from left to right. So, in your first example, you divide the 10/5 before you multiply the 4x5. In your second example you would subtract because it comes first when moving from left to right. However, you always do all the multiplication and division before doing any of the addition and subtraction. Jennie, who is not a math whiz, but loves order of operations. Quote Link to comment Share on other sites More sharing options...
Bokons Posted February 19, 2009 Author Share Posted February 19, 2009 Your posts have been a big help! Quote Link to comment Share on other sites More sharing options...
Dee in MI Posted February 20, 2009 Share Posted February 20, 2009 I have the same question about addition and subtraction, eg. 12-2+20. Would we do the 12-2 first, or the 2+20? Thanks for any help. If you understand this as 12 + (-2) + 20, then you can do it in any order that you want. All of the following will give the same answer: 12-2+20 -2+12+20 12+20-2 20+12-2 Since addition and multiplication can be done in any order (they are commutative), then you may see it more clearly if you understand subtraction as simply adding the negative of the number and division as multiplying by the reciprical. Then the order doesn't matter. Quote Link to comment Share on other sites More sharing options...
Bokons Posted February 20, 2009 Author Share Posted February 20, 2009 If you understand this as 12 + (-2) + 20, then you can do it in any order that you want. All of the following will give the same answer: 12-2+20 -2+12+20 12+20-2 20+12-2 Since addition and multiplication can be done in any order (they are commutative), then you may see it more clearly if you understand subtraction as simply adding the negative of the number and division as multiplying by the reciprical. Then the order doesn't matter. Yes, this makes sense. I hadn't thought of it this way. Thanks, Dee! Quote Link to comment Share on other sites More sharing options...
fractalgal Posted February 20, 2009 Share Posted February 20, 2009 Ds10 is using CLE math 4, and just started 408. The first lesson was order of operations (although CLE calls it a little differently). I am confused about whether to always do multiplication before division, or only when it comes before division when going left to right. For example, 12-10/5+4x5 (I had to use / for the division sign since my computer doesn't have it). Would we do the 4x5 first, or the 10/5 since it comes before the multiplication when going from left to right? I have the same question about addition and subtraction, eg. 12-2+20. Would we do the 12-2 first, or the 2+20? Thanks for any help. Think of it is 12 + -(10/5) + (4x5). It makes no difference whether you divide or multiply first if you think of it this way because you should get the same answer. Case 1: 12 + -(2) + 20 = 30 Case 2: 12 + 20 + -(2) = 30 We know that subtraction can be rewritten in terms of addition. Think of the product and quotient in parenthesis as having to be done first. Then you can add [or in the case of subtraction, add the opposite] the terms together in any order. Quote Link to comment Share on other sites More sharing options...
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