Please answer the questions belOw.

a) For an additional time series model, what does the term "residual variation" mean? Describe briefly its main constituents. b) Explain the moving average centering and why it is employed. C) Given a time series with trend figures already calculated, describe in words only, the method for calculating seasonal variation values using the additive model. When projecting a moving average trend, what basis would make the choice of the following appropriate? (i) Projecting 'by eye'. (ii) Using the method of semi-averages (iii) Using the average change in trend per period from the range d) Explain how management of an organisation might use seasonal variation figures and seasonally adjusted data.The following regression equation was calculated for a class of 24 CPA II students. Y = 3.1+ 0.021X, + 0.075X2 + 0.043X, Standard error (0.019) (0.034) (0.018) Whereby: Y = Standard score on a theory examination X, = Students rank (from the bottom) in high school X, = Students verbal aptitude score X. a measure of the students character Required: a) Calculate the t ratio and the 95% confidence interval for each regression coefficient. b) What assumptions did you make in (a) above? How reasonable are they? c) Which regressor gives the strongest evidence of being statistically discernible? d) In writing up a final report, should one keep the first regressor in the equation, or drop it? Why