(a) You obtain the following sample autocorrelations and partial autocorrelations for a sample of 100 observations from actual data:

Lag 1 2 3 4 5 6 7 acf 0.420 0.104 0.032 −0.206 −0.138 0.042 −0.018 pacf 0.632 0.381 0.268 0.199 0.205 0.101 0.096 Can you identify the most appropriate time-series process for this data?

(b) Use the Ljung–Box Q*

test to determine whether the first three autocorrelation coefficients taken together are jointly significantly different from zero.