Consider the following autocorrelation and partial autocorrelation coefficients estimated using 500 observations for a weakly stationary series, yt: Lag 1 2 34 4 5 acf 0.307 -0.013 0.086 0.031 -0.197 pacf 0.307 0.264 0.147 0.086 0.049 (a) Using a simple 'rule of thumb', determine which, if any, of the acf and pacf coefficients, are significant at the 5% level. Use both the Box-Pierce and Ljung-Box statistics to test the joint null hypothesis that the first five autocorrelation coefficients are jointly zero. (b) What process would you tentatively suggest could represent the most appropriate model for the series in part (a)? Explain your answer.