Question

In a survey, 13 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $32 and standard deviation of $20. Construct a confidence interval at a 95% confidence level.

Give your answers to one decimal place.

±

Answer 1

Solution :

Given that,

Point estimate = sample mean = = $32

sample standard deviation = s = $20

sample size = n = 13

Degrees of freedom = df = n - 1 = 13 - 1 = 12

At 95% confidence level the t is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

t /2,df = t0.025,12 = 2.179

At 95% confidance level of is,

  t/2,df * (s /n)

32 2.179 * (20 / 13)

32 12.1