In a study on infants, one of the characteristics measured was head circumference. The mean head circumference of 8 infants was 34.4 cm.
a. Assuming that head circumferences are normally distributed with standard deviation 2.1 cm, determine a 90% confidence interval for the mean head circumference of all infants.
b. Obtain the margin of err,r E, for the confidence interval you found in part (a)
c. Determine the sample size required to have a margin of error of 0.7 cm with a 95% confidence level.