dexterwilliams161
10.06.2020 •
Mathematics
Construct the indicated confidence interval for the difference between the two population means. Assume that the two samples are independent simple random samples selected from normally distributed populations. Do not assume that the population standard deviations are equal.
A paint manufacturer wished to compare the drying times of two different types of paint. Independent simple random samples of 11 cans of type A and 9 cans of type B were selected and applied to similar surfaces. The drying times, in hours, were recorded. The summary statistics are as follows.
Type A
x-bar1 = 75.7 hrs.
s1 = 4.5 hrs.
n1 = 11
Type B
x-bar2 = 64.3 hrs.
s2 = 5.1 hrs.
n2 = 9
Construct a 98% confidence interval for the difference for the mean drying time between paint A and paint B.
A. 6.08 hrs < μ1 - μ2 < 16.72 hrs
B. 5.85 hrs < μ1 - μ2 < 16.95 hrs
C. 5.78 hrs < μ1 - μ2 < 17.02 hrs
D. 5.92 hrs < μ1 - μ2 < 16.88 hrs
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Ответ:
Step-by-step explanation:
The formula for determining the confidence interval for the difference of two population means is expressed as
Confidence interval = (x1 - x2) ± z√(s²/n1 + s2²/n2)
Where
x1 = sample mean of type A paint
x2 = sample mean of type B paint
s1 = sample standard deviation type A paint
s2 = sample standard for type B paint
n1 = number of samples of type A paint
n2 = number of samples of type B paint
From the information given,
x1 = 75.7
s1 = 4.5
n1 = 11
x2 = 64.3
s2 = 5.1
n2 = 9
x1 - x2 = 75.7 - 64.3 = 11.4
√(s1²/n1 + s2²/n2) = √(4.5²/11 + 5.1²/9) = √4.709
Degree of freedom = (n1 - 1) + (n2 - 1)
df = (11 - 1) + (9 - 1) = 18
For the 98% confidence interval, the z score from the t distribution table is 2.552
Margin of error = 2.552√4.709 = 5.55
The upper boundary for the confidence interval is
11.4 + 5.55 = 16.95 hours
The lower boundary for the confidence interval is
11.4 - 5.55 = 5.85 hours
The correct option is
B. 5.85 hrs < μ1 - μ2 < 16.95 hrs
Ответ:
c
Step-by-step explanation: