A regression model to predict the price of diamonds included the following predictor variables: the weight of the stone (in carats where 1 carat = 0.2 gram), the color rating (D, E, F, G, H, or I), and the clarity rating (IF, VVS1, VVS2, VS1, or VS2).
(a) Identify the quantitative predictor variable(s).
(b) How many indicator variables would be included in the model in order to prevent the least squares estimation from failing?
(c) Write the proposed model form for predicting a diamond price.