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Explain the difference between the quantities ∑xiyiand ∑xi∑yi.Provide an example to show that, in general, those two quantities are unequal.

Short Answer

Expert verified

∑xiyi≠∑xi∑yi

Step by step solution

01

 Step 1. Given information.  

∑xiyiand∑xi∑yi

02

 Step 2. The difference between ∑xiyi  and ∑xi∑yi also provide an example to show that those two quantities are unequal

∑xiyiis the sum of products, where the individual corresponding values of two data sets are multiplied first, followed by the total sum.

∑xi∑yiis a sum product, which means that the individual data sets are added separately and then the final sum of the two data sets is multiplied.

Consider the following set:

xi=1,2,3,4and yi=4,3,2,1

role="math" localid="1652992532305" ∑xiyi=1×4+2×3+3×2+1×4∑xiyi=4+6+6+4∑xiyi=20

And

role="math" localid="1652992556394" ∑xi∑yi=1+2+3+4+4+3+2+1∑xi∑yi=1010∑xi∑yi=100

role="math" localid="1652992583289" ∑xiyi≠∑xi∑yi

As a result, ∑xiyi is the product of sums and ∑xi∑yi is the sum of sums.

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