Discussion:
Q: A researcher claims that the average age of a woman before he has her first child is now greater than it was in 1990. In 1990, that average age was 26.4 years. She obtains a random sample of 40 women who all recently gave birth to their first child, and calculates their mean age to be 27.1 years. From another recent study, she learns that the standard deviation among all women now giving birth to their first child is 6.4 years. Test her claim at the .05 level of significance.