In a survey, 17 people were asked how much they spent on their child's last birthday gift. The results are normally distributed with a mean of $39 and standard deviation of $20. Construct a confidence interval at a 90% confidence level.
(Please notice they want the answer in a form using midpoint and margin of error)
Answer: the confidence interval at a 90% confidence level for the amount spent on a child's last birthday gift is $30.6 to $47.4, with a midpoint of $39 and a margin of error of approximately $8.4.
