Answer:
(1) The point estimate for the population mean is 4.925.
(2) Therefore, a 95% confidence interval for the population mean pH of rainwater is [4.715, 5.135] .
(3) Therefore, a 99% confidence interval for the population mean pH of rainwater is [4.629, 5.221] .
(4) As the level of confidence increases, the width of the interval increases.
Step-by-step explanation:
We are given that the following data represent the pH of rain for a random sample of 12 rain dates.
X = 5.20, 5.02, 4.87, 5.72, 4.57, 4.76, 4.99, 4.74, 4.56, 4.80, 5.19, 4.68.
(1) The point estimate for the population mean is given by;
Point estimate, =
=
= = 4.925
(2) Let = mean pH of rainwater
Firstly, the pivotal quantity for finding the confidence interval for the population mean is given by;
P.Q. = ~
where, = sample mean = 4.925
s = sample standard deviation = 0.33
n = sample of rain dates = 12
= population mean pH of rainwater
<em> Here for constructing a 95% confidence interval we have used a One-sample t-test statistics as we don't know about population standard deviation. </em>
<u>So, 95% confidence interval for the population mean, </u><u> is ;
</u>
P(-2.201 < < 2.201) = 0.95 {As the critical value of t at 11 degrees of
freedom are -2.201 & 2.201 with P = 2.5%}
P(-2.201 < < 2.201) = 0.95
P( <
<
) = 0.95
P( <
<
) = 0.95
<u>95% confidence interval for</u> = [
,
]
= [ ,
]
= [4.715, 5.135]
Therefore, a 95% confidence interval for the population mean pH of rainwater is [4.715, 5.135] .
The interpretation of the above confidence interval is that we are 95% confident that the population mean pH of rainwater is between 4.715 & 5.135.
(3) Now, 99% confidence interval for the population mean, is ;<u>
</u>
P(-3.106 < < 3.106) = 0.99 {As the critical value of t at 11 degrees of
freedom are -3.106 & 3.106 with P = 0.5%}
P(-3.106 < < 3.106) = 0.99
P( <
<
) = 0.99
P( <
<
) = 0.99
<u>99% confidence interval for</u> = [
,
]
= [ ,
]
= [4.629, 5.221]
Therefore, a 99% confidence interval for the population mean pH of rainwater is [4.629, 5.221] .
The interpretation of the above confidence interval is that we are 99% confident that the population mean pH of rainwater is between 4.629 & 5.221.
(4) As the level of confidence increases, the width of the interval increases as we can see above that the 99% confidence interval is wider as compared to the 95% confidence interval.