Mean and standard deviation for linear combinations

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SUMMARY

The discussion focuses on calculating the mean (ybar) and standard deviation (Sy) for the linear transformation of a dataset X, where the mean xbar is 100 and the standard deviation Sx is 10. The transformation is given by the equation 2(Yi - 5)/10 + 7, which simplifies to Yi = 5Xi - 30. The established formulas for linear transformations indicate that ybar can be calculated as ybar = a(xbar) + b and Sy as Sy = aSx, where a and b are constants derived from the transformation.

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Homework Statement



Data set in X with mean xbar = 100 and standard deviation Sx = 10

Find ybar and Sy for 2(Yi-5)/10 + 7



Homework Equations





The Attempt at a Solution



All the problems I have seen are in the form yi = axi + b in which case the mean ybar = a(xbar) + b and Sy = aSx

What does Yi represent exactly? How does it relate to xi?
 
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I don't see how you can find ybar and Sy unless you know the relationship between X and Y.

You show an expression 2(Yi - 5)/10 + 7 = (Yi - 5)/5 + 7. Could this be Xi?

If that's the case, then you can solve for Yi.

Xi = (Yi - 5)/5 + 7
==> Xi - 7 = (Yi - 5)/5
==> 5(Xi - 7) = (Yi - 5)
==> 5(Xi - 7) + 5 = Yi
or
Yi = 5Xi - 30
 

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