Question

Use the paired t-interval procedure to obtain the required confidence interval. You may assume that the conditions for using the procedure are satisfied. Ten different families are selected at random. The amount of water each family uses per day before and after viewinga conservation video is recorded. The amounts (in gallons) are shown below. Before 33 33 38 33 35 35 40 40 40 31 After 34 28 25 2835 33 31 28 35 33 Determine a 90% confidence interval for the difference between the mean numbers of gallons of water used per day before and after viewing the video. O 3.8 to 5.8 gallons O 2.5 to 7.1 gallons O 1.5 to 8.1 gallons O 1.8 to 7.8 gallons

Answer 1

solution:-

=> d = -1,5,13,5,0,2,9,12,5,-2

Xd = 4.8, s = 5.2451, n = 10, df = 9, 90% confidence interval

t = 1.833

90% confidence interval for the difference between the mean = X +/- t*s/sqrt(n)
= 4.8 +/- 1.833*5.2451/sqrt(10)
= 1.7597 , 7.8402
= 1.8 , 7.8 (rounded)

==> option D.