Ambiguous question in homework...

Hi All,

I just wanted to probe this board before I went to the TA, as class just started and I don't want to be *that* guy.

Anyway, I have an iid set of results and I'm given a known mean, and I calculate the variance. Fair enough.

Then I am given an equation akin to a regression line based on another variable, and told to calculate the variance as if this equation were correct. Also pretty simple.

Then I do regression and calculate the errors. The next question says "How do I estimate the variance from the residuals". Any thoughts?