• Researching the fluctuations in the amount of gas sold (Q: cylinder) depending on the gas price (PG: 1000VND/cylinder), some people think that gas quality is important, that person thinks that during the months when the dealer imports cylinders The amount of new gas sold is not the same as the months when old gas cylinders are imported, so the regression model has the following variables: D = 1 for months when new gas cylinders are imported, D = 0 for other months, DPG = D * PG. Indicate = 5%. Dependent Variable : Q Method : Least Squares Date: 12/01/10 Time: 20:17 Sample: January 1997 March 1999 Included observation: 27 Variable Coeficient Std. Error T –Statistic Prob C 2403.55 564.01 PG -7.0673 0.20832 D 106.01 98.54 DPG 0.278 0.0789 R –squared 0.99252 Mean dependent var 1831.4 Adjusted R – squared 0.99154 SD dependent var SE of regression 41.568 A kaike info criterion Sum squared residual 39741 Schwarz criterion Log likelihood F – satistic 1016.8 Durbin – Watson stat 1.9506 Prob (F – statistic) a) Write an overall regression function and a sample regression function for each case of month of sale of new and used gas cylinders. b) In the month of selling new gas cylinders, if the gas price is 110 thousand VND, what is the estimated sales volume? For the month of selling old gas cylinders, how much is that value? c) Are the model coefficients significantly different from zero? d) Is the intercept coefficient of the model in the months of importing new cylinders and old cylinders really different? e) Is the regression function appropriate? f) Some people think that adding dummy variables is not very reasonable. Would you please check that opinion? g) When the price is reduced by 1 thousand VND, what is the difference in the ability to sell more between old and new gas cylinders? h) One person believes that because gas cylinders are always high priced and safe, sales volume is not influenced by the quality of gas cylinders but by advertising. He believes that in months with active advertising, sales increase more than in months without active advertising. Build a model and show how to test it. i) If we want to consider the simultaneous impact of both importing new or old gas cylinders and whether there is active advertising or not, how should we build a model and perform tests?