In a survey, 21 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $41 and standard deviation of $18. Construct a confidence interval at a 95% confidence level.
Give your answers to one decimal place.
___________ ± ____________
95% means withing 2σ of the mean, right?
If so, then you want
µ-2σ <= x <= µ+2σ