Question

The average annual cost of the first year of owning and caring for a large dog is $1,843 (US News and World Report, September 9, 2013). The Irish Red and White Setter Association of America has requested a study to estimate the annual first-year cost for owners of this breed. A sample of 50 will be used. Based on past studies, the population standard deviation is assumed known with σ ? = $255. a. What is the margin of error for a 95% confidence interval of the mean cost of the first year of owning and caring for this breed (to 2 decimals)? b. The DATAfile Setters contains data collected from fifty owners of Irish Setters on the cost of the first year of owning and caring for their dogs. Use these data sets to compute the sample mean (to 2 decimals). Using this sample, what is the 95% confidence interval for the mean cost of the first year of owning and caring for an Irish Red and White Setter (to 2 decimals)?

Answer 1

Answer:

a. Error is 0.14

b. between 1913.68 to 1772.32

Step-by-step explanation:

Requirement a)

The margin of error is a statistic expressing the amount of random sampling error in a survey's results.

Given,

Size of the sample n = 50

We know, At 95% confidence interval,

The margin of error,

= 0.98/√n  

= 0.98/√50

= 0.98/7.07

= 0.13859 ~ 0.14

So the margin of error at 95% confidence level is 0.14.

Requirement b)

Given,

Standard deviation σ = 255

Population mean z = 1814

Size of the sample n = 50

We know, At 95% confidence interval,

(z-µ)/(σ/√n)  < Z_0.05

= - Z_0.05 < (z-µ)/(σ/√n) < Z_0.05

= - 1.96 * σ/√n < (z-µ)/(σ/√n)*  σ/√n  < 1.96 * σ/√n  [ in two tail Z test the value of Z_0.05 is 1.96 ]

= - 1.96 * 255/√50 < Z-µ <  1.96 * 255/√50

= -70.6828 < Z-µ < 70.6828

= 70.6828 > µ - Z > -70.6828

= 70.6828 + Z > µ > -70.6828 + Z

= 70.6828 + 1814 > µ > -70.6828 + 1814

=1913.68 > µ > 1772.32

So, the sample mean would be between 1913.68 to 1772.32.