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Topic: Re: WS/Test Unit 2 error
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Al Coons

Posts: 898
Registered: 12/4/04
Re: WS/Test Unit 2 error
Posted: Oct 21, 1996 11:52 AM
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Ron Dirkse pointed out an error in problem 6 of the test I posted the other
day. Actually it was correct on the test my students took, but I entered it
incorrectly when trying to convert to an ASCII version for posting (nice
excuse Al). The first formula below should be y = a + bx, rather than ax +

>6. Your AP STATS formula sheet has the following three formulas which relate
>to linear regression.
> y = ax + b, b = r *s(y)/s(x), a = y-mean - b(x-mean)
> Show that the regression line always contains the point (x-mean, y-mean)

Ron asked if I did expected an algebraic solution. Yes - about 80% of the
students did it correctly.

Thanks Ron,


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