In: Math
For large U.S. companies, what percentage of their total income comes from foreign sales? A random sample of technology companies (IBM, Hewlett-Packard, Intel, and others) gave the following information.†
| Technology companies, % foreign revenue: x1; n1 = 16 | |||||||
| 62.8 | 55.7 | 47.0 | 59.6 | 55.3 | 41.0 | 65.1 | 51.1 |
| 53.4 | 50.8 | 48.5 | 44.6 | 49.4 | 61.2 | 39.3 | 41.8 |
Another independent random sample of basic consumer product companies (Goodyear, Sarah Lee, H.J. Heinz, Toys 'R' Us) gave the following information.
| Basic consumer product companies,% foreign revenue: x2; n2 = 17 | |||||||||
| 28.0 | 30.5 | 34.2 | 50.3 | 11.1 | 28.8 | 40.0 | 44.9 | ||
| 40.7 | 60.1 | 23.1 | 21.3 | 42.8 | 18.0 | 36.9 | 28.0 | ||
| 32.5 | |||||||||
Assume that the distributions of percentage foreign revenue are mound-shaped and symmetric for these two company types.
(a) Use a calculator with mean and standard deviation keys to calculate x1, s1, x2, and s2. (Round your answers to two decimal places.)
| x1 = | % |
| s1 = | % |
| x2 = | % |
| s2 = | % |
(b) Let μ1 be the population mean for
x1 and let μ2 be the
population mean for x2. Find a 98% confidence
interval for μ1 − μ2.
(Round your answers to two decimal places.)
| lower limit | % | |
| upper limit | % |
| Technology companie ( X ) | Σ ( Xi- X̅ )2 | consumer product ( Y ) | Σ ( Yi- Y̅ )2 | |
| 62.8 | 124.0996 | 28 | 31.36 | |
| 55.7 | 16.3216 | 30.5 | 9.61 | |
| 47 | 21.7156 | 34.2 | 0.36 | |
| 59.6 | 63.0436 | 50.3 | 278.89 | |
| 55.3 | 13.2496 | 11.1 | 506.25 | |
| 41 | 113.6356 | 28.8 | 23.04 | |
| 65.1 | 180.6336 | 40 | 40.96 | |
| 51.1 | 0.3136 | 44.9 | 127.69 | |
| 53.4 | 3.0276 | 40.7 | 50.41 | |
| 50.8 | 0.7396 | 60.1 | 702.25 | |
| 48.5 | 9.9856 | 23.1 | 110.25 | |
| 44.6 | 49.8436 | 21.3 | 151.29 | |
| 49.4 | 5.1076 | 42.8 | 84.64 | |
| 61.2 | 91.0116 | 18 | 243.36 | |
| 39.3 | 152.7696 | 36.9 | 10.89 | |
| 41.8 | 97.2196 | 28 | 31.36 | |
| 32.5 | 1.21 | |||
| Total | 826.6 | 942.7176 | 571.2 | 2403.82 |
Mean X̅ = Σ Xi / n
X̅ = 826.6 / 16 = 51.66
Sample Standard deviation SX = √ ( (Xi - X̅ )2 / n - 1 )
SX = √ ( 942.7176 / 16 -1 ) = 7.93
Mean Y̅ = ΣYi / n
Y̅ = 571.2 / 17 = 33.6
Sample Standard deviation SY = √ ( (Yi - Y̅ )2 / n - 1 )
SY = √ ( 2403.82 / 17 -1) = 12.26
Part a)
X1 = 51.66
S1 = 7.93
X2 = 33.60
S2 = 12.26
Part b)
Confidence interval :-
t(α/2, DF) = t(0.02 /2, 27 ) = 2.473

DF = 27

Lower Limit =
Lower Limit = 9.23
Upper Limit =
Upper Limit = 26.90
98% Confidence interval is ( 9.23 , 26.90 )