Then, RA = JA 187 178 = 1.05, TA STA = nA - 1 = Cry? - 2RA CityI + RA Ex? nA - 1 4463 - 2(1.05) (4245) + (1.05)2(4066) = 10 - 1 Similarly, we have for company B: Ey = 46, Ly? = 316.3, [= = 78, Ex = 876, [ myI = 452, and RB = yB TB ST.B = nB - 1 Therefore, we have Y separate = WARAXA + WBRBXB Var (Y separate) = Wh (1 - NA NB ST, B NA STA + WB (1 - NA NB NB Using previous data and results, the combined ratio estimate can be easily obtained. X = XA + XB NA + NB Xst = ist = WALA + WBIB = Yst = Ust = WAYA + WByB = Rcombined = rc = yst Ist Ycombined = Rcombined * = In order to estimate the variance, Var(Jcombined) = _JA ) WA{SA - 2 RcombinedPASyASIA + Rcombined SZA } + Discuss which estimator is better? State your reasons