Question

The number of active coal mines in Utah has steadily decreased since 1960. However, peak production occurred in 2001. One measure of mine productivity is tons/employee hour. In a random sample of 40 days, the mean tons/employee hour was 4.97. Assume σ = 1.16. Find a 95% confidence interval for the true mean tons/employee hour. (Round your answers to four decimal places.)

____________, _____________ tons/employee hour

Answer 1

Solution :

Given that,

Sample size = n = 40

Z_/2 = 1.96

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

= 1.96 * (1.16 / 40 )

= 0.3595

At 95% confidence interval estimate of the population mean is,

- E < < + E

4.97 - 0.3595 < < 4.97 + 0.3595

4.6105 < < 5.3295

4.6105 , 5.3295 tons/employee hour