The lengths of pregnancies in a small rural village are normally distributed with a mean of 269 days and a
standard deviation of 12 days.
15.[2] In what range would you expect to find the middle 50% of most
pregnancies? Round your answer to the nearest tenth of a day.
16.[3] If you were to draw samples of size 37 from this population, in what
range would you expect to find the middle 50% of most averages for
the lengths of pregnancies in the sample? Round to the nearest tenth.
In a survey, 18 parents were asked how much they spent on their child's last birthday gift. The results were
roughly bell-shaped with a mean of $34 and standard deviation of $15.
17.[3] Construct a confidence interval at a 90% confidence level.
18.[2] Interpret the confidence interval. Select all correct interpretations.
Fill in the blanks for the interpretations you select.
A.) The mean amount spent by parents on their child's birthday gift is between
and
90% of the time. We know this is true because the mean of our sample is between those values.
B.) There is a 90% chance that the mean expense for the population of parents when buying a
birthday gift for their child is between
and
C.) With 90% confidence, the mean amount spent by all parents on their child's birthday gift is
between
and
D.) There is a 90% chance that the mean amount spent by a sample of 18 parents on their child's
birthday gift will be between
and
E.) With 90% confidence, the mean amount spent by a randomly selected parent on their child's
birthday gift will be between
and