Resistance observations (ohms) for subgroups of a certain type of register gave the following summary quantities:

i ni x i si i ni x i si 1 4 430.0 22.5 7 4 420.8 25.4 2 4 418.2 20.6 8 4 431.4 24.0 3 3 435.5 25.1 9 4 428.7 21.2 44427.6 22.3 10 4 440.1 25.8 5 4 444.0 21.5 11 4 445.2 27.3 6 3 431.4 28.9 12 4 430.1 22.2

(continued)

i ni x i si i ni x i si 13 4 427.2 24.0 17 3 447.0 19.8 144 439.6 23.3 18 4 434.4 23.7 15 3 415.9 31.2 19 4 422.2 25.1 16 4 419.8 27.5 20 4 425.7 24.4 Construct appropriate control limits. [Hint: Use x

nixi/
ni and s2

(ni  1)s2 i /
(ni  1).]