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Answer:
The critical value that should be used in constructing the interval is T = 5.8408.
The 99% confidence interval for the true mean yield is between 2.943 bushels per acre and 96.268 bushels per acre.
Step-by-step explanation:
We have the standard deviation of the sample, so we use the students t-distribution to solve this question.
The first step to solve this problem is finding how many degrees of freedom, we have. This is the sample size subtracted by 1. So
df = 4 - 1 = 3
99% confidence interval
Now, we have to find a value of T, which is found looking at the t table, with 3 degrees of freedom(y-axis) and a confidence level of . So we have T = 5.8408. This is the critical value.
The margin of error is:
M = T*s = 5.8408*7.99 = 46.668 bushels per acre
In which s is the standard deviation of the sample.
The lower end of the interval is the sample mean subtracted by M. So it is 49.6 - 46.668 = 2.943 bushels per acre.
The upper end of the interval is the sample mean added to M. So it is 49.6 + 46.668 = 96.268 bushels per acre.
The 99% confidence interval for the true mean yield is between 2.943 bushels per acre and 96.268 bushels per acre.