A car dealership owner created a data table to see how many new and used cars were sold over several months.
2 answers:
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Answer:
a: Sample mean: 20, Sample standard deviation: 1.732
b: 19.13 <µ < 20.87
c: 18.84< µ < 21.16
d: as the confidence level increases, the interval becomes wider
Step-by-step explanation:
a: Sample mean is found by adding up all the individual values of the sample, then dividing by the total number of values in the sample.
Sample standard deviation is the square root of the variance
See the first attached photo for the calculations of these values.
We need to create a 80% confidence interval for the population. Since n < 30, we will use a t-value with degree of freedom of 7 (the degree of freedom is always one less than the sample size.
Look for the column on the t-distribution chart that has "area in two tails" of 0.20 (80%), and row 7 (degree of freedom)
The t-value is 1.415
See the second attached photo for the construction of the confidence interval
We need to create a 90% confidence interval for the population. Since n < 30, we will use a t-value with degree of freedom of 7 (the degree of freedom is always one less than the sample size.
Look for the column on the t-distribution chart that has "area in two tails" of 0.10 (90%), and row 7 (degree of freedom)
The t-value is 1.895
See the third attached photo for the construction of the confidence interval
