a) The error made is numerically less than 0.4 mm
Therefore, P(|z| less than 0.4)
b) Given that the body length of a butterfly is measured nine times with the instrument, calculate, to three decimal places, the probability that the mean of the nine readings will be within 0.5mm of the true length.
1st: P(|z| less than 0.5) ... this is the probability for one time.
2nd: Let, P(|z| less than 0.5)= . Therefore, the probability is
c) Sorry.... I don't know what is confidence interval...