STAT Homework Help!

Question

In a survey, 29 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $40 and standard deviation of $7. Find the margin of error at a 80% confidence level.

Give your answer to two decimal places.

Answer 1

An 80% confidence interval for the mean (n-1 degrees of freedom) is

xbar +/- t critical value * s/sqrt(n)

InvT(0.10, 28) = -1.3125

40 +/- 1.3125*(7/sqrt(29))

Margin of error is 1.3125*(7/sqrt(29)) = 1.706