Question

In a survey, 15 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $48 and standard deviation of $7. Construct a confidence interval at a 90% confidence level.

Give your answers to one decimal place.

___±_____

Answer 1

Solution :

degrees of freedom = n - 1 = 15 - 1 = 14

t/2,df = t0.05,14 = 1.761

Margin of error = E = t/2,df * (s /n)

= 1.761 * (7 / 15)

Margin of error = E = 3.2

The 90% confidence interval estimate of the population mean is,

  ± E  

= 48  ± 3.2

= ( 44.8, 51.2 )