Question

1. In a random sample of 44 downloadable books from a website, the mean cost is $8.58 with a standard deviation of $2.09.

Which interval is the 95% confidence interval for the mean cost of all the downloadable books on the website?

($7.96, $9.20)

($7.77, $9.35)

($8.39, $8.77)

($8.26, $8.90)

2.) In a random sample of 80 students in first grade, the mean hours of sleep per night was 9.4 with a standard deviation of 0.41. In a random sample of 50 students in 12th grade, the mean hours of sleep per night was 7.5 with a standard deviation of 0.52.

Which interval is a 99% confidence interval for the difference between the mean hours of sleep?

(1.75 h, 2.05 h)

(1.89 h, 1.91 h)

(1.43 h, 2.37 h)

(1.68 h, 2.12 h)

Answer 1

The solution is done showing all steps with calculation and necessary formulas. For better understanding a value table is also attached. Hope you can understand.

z-table -