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# Sigma Notation Part 2

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17
Next I want to introduce you to a little tweak with sigma notation. I told you before that we’re going to add up whatever comes in those parentheses. But I also mentioned we could do operations within those parentheses. We could give you some instructions to say modify every score before you add them up. The only thing I want to mention here is order of operations. In order of operations, you always do parentheses first. Parentheses are the very first thing you do when doing any math. So just as a reminder, if I’m going to tell you to do something to every score in those parentheses, I need to do that first. Let’s give a really simple example.
55.3
Let’s say I told you to give the sum of x minus 1. Because that x minus 1 comes in the parentheses, you’re going to subtract 1 from every score first and then add them up. So let’s take a look at this in action. So in this case, this would say subtract 1 from every x. And remember, x is a set of numbers, those four ages. So this would say subtract 1 from 30, 21, and so on, and so forth. And I’m going to subtract that 1 from every score and then add them up. So that’s going to give me a total sum of 151.
87.1
So very minor modification to the procedure I showed you for basic sigma notation, but it makes sigma notation very flexible. I can do whatever I want in those parentheses. Just remember, parentheses first.