In a sample of 100 steel wires the average breaking strength is 50 kN, with a standard deviation of 2 kN.
a. Find a 95% confidence interval for the mean breaking strength of this type of wire.
b. An engineer claims that the mean breaking strength is between 49.7 kN and 50.3 kN. With what level of
confidence can this statement be made?
c. How many wire must be sampled so that a 95% confidence interval specifies the mean breaking strength
to within ±0. 3 kN?
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