Question

In a survey, 30 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $35 and standard deviation of $17. Construct a confidence interval at a 95% confidence level.

Answer 1

CI 95 % = ( 28.92 ; 41.08 )

Explanation:

Sample Information:

sample size n = 30

sample mean = 35 %

sample standard deviation s = 17

To construct a CI 95 %

significance level is α = 5 % α = 0.05 α/2 = 0.025

z critical for α/2 from z- table is : z (c) = 1.96

CI 95 % = ( x ± z(c) * s/√n )

CI 95 % = ( 35 ± 1.96 * 17/√30 )

CI 95 % = ( 35 ± 6.08 )

CI 95 % = ( 28.92 ; 41.08 )