I’ve been getting this question wrong on homework assignments and tests and for the life of my, I cannot find anywhere in the chapter where it tells me how to compute it. We are working on least-squares line in our stats class and I get the jist of what we are talking about and how to compute the slope with yhat and all that but a single question, worded differently but worked the same has me stumped. I draw out my least-sqaures graph and then the next question reads: The calves you want to buy are 12 weeks old. What does the least-squares line predict for a healthy weight for a 12-week old calf? Show your work" I don’t know what I have to do to compute what the healthy weight would be. Does anyone know if it’s a formula I use because I’m supposed to answer to the nearest decimal and obviously if I’m looking at a graph I constructed myself and how incorrect (to the nearest decimal anyway) hand made graphs are, I can only guess if the weight is 100.34 or something. If she wants it as accurate as possible and wants me to show my work she wants me to use something to compute it. Can anyone help me on this?

So you’ve got a line, y=mx+b ? Why don’t you just plug in 12 weeks for x?

Can you use the same thing when you find a regular slope? I thought it would be different with this formula or else why wouldn’t they use the same one? This one is yhat=a+bx

It’s the same formula. Rewrite it as “yhat=bx+a” and then change the letters. The thing with stats is that everyone uses their own symbols and terminology. I prefer y=mx+b because that’s what I learned first. Like the symbol for mean can be: M, m, mu (if population), x-bar, y-bar, etc… depending on which text you can use. And I now know of four different methods for doing a one-way analysis of variance, thanks to multiple books.

y_hat is the predicted value of y at x. If you don’t get that, then you need to go back and review until you do.