Question

In a survey, 25 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $45 and standard deviation of $9. Construct a confidence interval at a 80% confidence level. Give your answers to one decimal place.

Answer 1

Solution :

Given that,

Z/2 = Z_0.10 = 1.282

Margin of error = E = Z/2 * ( /n)

= 1.282 * ( 9 /  25 )

= 2.3

At 80% confidence interval estimate of the population mean is,

  ± E   

= 45  ± 2.3

= ( $ 42.7, $ 47.3 )