In: Math
David E. Brown is an expert in wildlife conservation. In his book The Wolf in the Southwest: The Making of an Endangered Species (University of Arizona Press), he records the following weights of adult grey wolves from two regions in Old Mexico.
Chihuahua region: x1 variable in pounds
86 | 75 | 91 | 70 | 79 |
80 | 68 | 71 | 74 | 64 |
Durango region: x2 variable in pounds
68 | 72 | 79 | 68 | 77 | 89 | 62 | 55 | 68 |
68 | 59 | 63 | 66 | 58 | 54 | 71 | 59 | 67 |
(a) Use a calculator with mean and standard deviation keys to calculate x1, s1, x2, and s2. (Use 2 decimal places.)
x1 | |
s1 | |
x2 | |
s2 |
(b) Let μ1 be the mean weight of the population
of all grey wolves in the Chihuahua region. Let
μ2 be the mean weight of the population of all
grey wolves in the Durango region. Find a 99% confidence interval
for μ1 – μ2. (Use 2 decimal
places.)
lower limit | |
upper limit |
Values ( X ) | Σ ( Xi- X̅ )2 | Values ( Y ) | Σ ( Yi- Y̅ )2 | |
86 | 104.04 | 68 | 1.3612 | |
75 | 0.64 | 72 | 26.6948 | |
91 | 231.04 | 79 | 148.0286 | |
70 | 33.64 | 68 | 1.3612 | |
79 | 10.24 | 77 | 103.3618 | |
80 | 17.64 | 89 | 491.3626 | |
68 | 60.84 | 62 | 23.3608 | |
71 | 23.04 | 55 | 140.027 | |
74 | 3.24 | 68 | 1.3612 | |
64 | 139.24 | 68 | 1.3612 | |
59 | 61.3606 | |||
63 | 14.6942 | |||
66 | 0.6944 | |||
58 | 78.0272 | |||
54 | 164.6936 | |||
71 | 17.36 | |||
59 | 61.3606 | |||
67 | 0.0278 | |||
Total | 758 | 623.6 | 1203 | 1336.5002 |
Mean X̅ = Σ Xi / n
X̅ = 758 / 10 = 75.8
Sample Standard deviation SX = √ ( (Xi - X̅
)2 / n - 1 )
SX = √ ( 623.6 / 10 -1 ) = 8.32
Mean Y̅ = ΣYi / n
Y̅ = 1203 / 18 = 66.83
Sample Standard deviation SY = √ ( (Yi - Y̅ )2 / n - 1
)
SY = √ ( 1336.5002 / 18 -1) = 8.87
part a)
X1 = 75.8
S1 = 8.32
X2 = 66.83
S2 = 8.87
Part b)
Confidence interval :-
t(α/2, DF) = t(0.01 /2, 19 ) = 2.861
Lower Limit =
Lower Limit = -0.65
Upper Limit =
Upper Limit = 18.58
99% Confidence interval is ( -0.65 , 18.58
)