Answer:
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
= 8 
, since she can't buy half a CD, she's limited to no more than 8 CDs. If x = the cost of one CD, then x CDs cost $18x. Since we are limited to $153, our equation looks like... 18x < 153x < 8