The average weight at birth of babies whose mothers are consuming cocaine is estimated in a study. Suppose that the birth weight is normally distributed with a standard deviation of 350 grams.
a) What is the sample size needed to estimate the average weight with a maximum error of 0.5 lbs at a level of confidence of 95%? Note: (1lb = 454g)
b) Let's say we collect a random sample of infants and that we compute a 95% confidence interval for the population mean weight. If we change the level of confidence from 95% to 98% would the length of the interval be shorter, longer or not change? Explain.