Guys,
Beautifully calculated, and your intuition on #3 is right on. One tiny issue: the coefficients I had calculated did not include the 90%, 5% and 5% weighting. I just added that to my raw data and suggested that you could plug it into the regression after I left if you wanted. Sorry for the confusion. It turns out that the 90/5/5 weighting has almost exactly the same fit (> .91 R-squared), so I went ahead and substituted the correct coefficients.
Another thing to note, just to keep in mind for the final, etc. To calculate confidence interval of the entire equation (not just a single coefficient), you have to multiple standard error by SQRT(1 + (1/N)). Also, we should be using the T-value here since we only have 48 observations. (It doesn't make a huge difference in calculation, but it's a more correct approach.)
Can someone print the revised assignment and turn in? The last tab in the spreadsheet has the new numbers. I have a feeling I might oversleep and/or skip stats once again.
--D