9. For the population of infants subjected to fetal surgery for congenital anomalies the distri- bution of gestational ages at birth is approximately normal with mean u and standard de- viation o. A...

Please exclude (b)

Extracted text: 9. For the population of infants subjected to fetal surgery for congenital anomalies the distri- bution of gestational ages at birth is approximately normal with mean u and standard de- viation o. A random sample of 15 such infants has a mean gestational age x = and a standard deviation s = 3.2 weeks. 30.2 weeks era (a) Construct a 95% confidence interval for the true population mean u. (b) What is the length of this interval? (c) How large a sample would be required for the 95% confidence interval to have length 3 weeks? Assume that the population standard deviation o is known and that or = 3.6 weeks. (d) How large a sample would be needed for the 95% confidence interval to have length 2 weeks?