To solve for the confidence interval for the true average
percentage elongation, we use the z statistic. The formula for confidence
interval is given as:
Confidence interval = x ± z σ / sqrt (n)
where,
x = the sample mean = 8.63
σ = sample standard deviation = 0.79
n = number of samples = 56
From the standard distribution tables, the value of z at
95% confidence interval is:
z = 1.96
Therefore substituting the known values into the
equation:
Confidence interval = 8.63 ± (1.96) (0.79) / sqrt (56)
Confidence interval = 8.63 ± 0.207
Confidence interval = 8.42, 8.84
<span> </span>