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# Summation Notation

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Im having trouble with summation notation. I dont know how to find the value of a certain variable for example. This is giving me lots of trouble and I have no idea what to do.

If you could help me figure out what to do that would be great.

Thank you.

Sep 1, 2015

#1
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At the bottom of the summation it indicates what it starts on, in this case i starts on 1. At the top of the summation it tells you what the maximum number is that i gets up to. Now you need to sum every number from what you start on up till the maximum.

Your 1st sum translates to $$x_1+x_2+x_3+x_4+x_5+x_6=15$$Your 2nd sum translates to $$x_1+x_2+x_3+x_4+x_5=20$$Your 3rd sum translates to $$\frac{x_1+x_2+x_3+x_4+x_5+x_6+x_7}{7}=8$$

Hope you should be able to do the rest of the problem now =)

Sep 2, 2015

#1
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Your 1st sum translates to $$x_1+x_2+x_3+x_4+x_5+x_6=15$$Your 2nd sum translates to $$x_1+x_2+x_3+x_4+x_5=20$$Your 3rd sum translates to $$\frac{x_1+x_2+x_3+x_4+x_5+x_6+x_7}{7}=8$$