Question

In a survey, 17 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 $10. Construct a confidence interval at a 80% confidence level.

Give your answers to one decimal place.

____+-_____

Answer 1

Given that, sample size ( n ) = 17

sample mean = $40 and

sample standard deviation ( s ) = $10

confidence level = 80% = 0.80

=> significance level = 1 - 0.80 = 0.20

t-critical value at significance level of 0.20 wit degrees of freedom = 17 - 1 = 16 is,

Margin of error is,

The 80% confidence interval for population mean is,

Answer: 40 ± 3.2