4) In a univariate linear regression, explain intuitively, graphically and mathematically, how the variance of the estimated slope depends on a) the number of observations; (2 marks) b) the mean squared deviation of the independent variable; (2 marks) c) BONUS: What else does it depend on? Can you explain how? (2 possible bonus marks) 5) Explain using both intuition and mathematics how a perfect correlation between two independent variables makes the estimation of coefficients impossible. (4 marks)