Question

Diameter measurements were logged as three independent data sets from the population of spherical steel bids produced in similar conditions. The following statistics parameters were evaluated:

- 28; d 5.5 mm; Sd1 0.3 mm; N2-30; d2 -5.7 mm; sd2 - 0.25 mm; N3 -15; d3 -5.3 mm; sd3 - 0.33 mm

N1=28, d1(bar)=5.5 mm, s_d1=0.3 mm;
N2=30, d2(bar)=5.7 mm, s_d2=0.25 mm;
N3=15, d3(bar)=5.3 mm, s_d3=0.33 mm

Neglecting systematic errors and other errors other than variation in the measured data set, calculate:
(a) An estimate of the pooled mean value of the diameter:
(b) The range in which the true mean should lie within 95% confidence:

Answer 1

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