10.108 In a study conducted by the Water Resources Research Center and analyzed by the Laboratory for Interdisciplinary Statistical Consulting at Virginia Tech, two different wastewater treatment plants are compared. Plant
𝐴
is located where the median household income is below $22,000 a year, and plant
𝐵
is located where the median household income is above $60,000 a year. The amount of waste-water treated at each plant (thousands of gallons/day) was randomly sampled for 10 days. The data are as follows:
Plant A:
21 19 20 23 22 28 32 19 13 18
Plant B:
20 39 24 33 30 28 30 22 33 24
Plant A:
21 19 20 23 22 28 32 19 13 18
Plant B:
20 39 24 33 30 28 30 22 33 24
Can we conclude, at the 5% level of significance, that the average amount of wastewater treated at the plant in the high-income neighborhood is more than that treated at the plant in the low-income area? Assume normality.
10.109 The following data show the numbers of defects in 100,000 lines of code in a particular type of software program developed in the United States and Japan. Is there enough evidence to claim that there is a significant difference between the programs developed in the two countries? Test on means. Should variances be pooled?
U.S. 48 39 42 52 40 48 52 52
54 48 52 55 43 46 48 52
Japan 50 48 42 40 43 48 50 46
38 38 36 40 40 48 48 45
U.S. 48 39 42 52 40 48 52 52
54 48 52 55 43 46 48 52
Japan 50 48 42 40 43 48 50 46
38 38 36 40 40 48 48 45