3.

(a)(i) mean=30.27 SD=0.88 (ii) mean=30.55 SD=1.19

(b) Since the SD of machine G is smaller than that of machine H, machine G is more consistent in production.

4.

(a)(i) mean=288.67 SD=78.39 (ii) mean=422 SD=83.76

(b) The mean maintenance charges of model S is lower than that of model T. The maintenance charges for model S is also more consistent than that of model T.