The first slide is the denifition of simple linear regression model, the second slides is an example [![definition][1]][1] The second question I have is I still have difficulties in understanding Confidence interval for mean and Confidence interval and Prediction interval. For the example above, if I was correct,the standard deviation would be 0.0634 then y3 would be :y3~(10,0.0634^2), so we can say we are 95% sure y3 would be from 10-20.0634 to 10+20.0634, why we still need Confidence interval for mean and and Prediction interval? Why we can't just use standard deviation s from sample directly