For data from 2005 to 2011 from Facebook on y =

number of people (in millions) worldwide using Facebook, the prediction equation ˆy = 2.13(2.72)x fits well, where x = number of years since January 1, 2005.

(a) Predict the number using the Internet at the beginning of (i) 2005 (take x = 0), (ii) 2011.

(b) Interpret the estimate 2.72.

(c) Illustrate the dangers of extrapolation, by predicting y on January 1, 2015.

(d) The straight-line model fitted to the data gives ˆy =

−114 + 95x. Explain why this model is inappropriate for these data.