Question 1203420
sample size is 64.
mean number of car accidents per year was 3.2 and sample standard deviation was .8.


t-score is indicated because the standard deviatiion is from the sample rather than from the population.


90% two tailed confidence interval has critical t-score with 63 degrees of freedom (sample size minus 1) equal to plus or minus t = 1.6694.


raw score is based on t-score formula of t = (x-m)/s.
t is the t-score.
m is the population mean.
s is the standard error.
solve for x to get the raw score.


standard error = sample standard deviation / sqrt(sample size) = .8/sqrt(64) = .8/8 = .1.



on the low side of the confidence interval, you get -1.6694 = (x-3.2)/.1.
solve for x to get x = .1 * -1.6694 + 3.2 = 3.03306.


on the high side of the confidence interval, you get 1.6694 = (x-3.2)/.1.
solve for x to get x = .1 * 1.6694 + 3.2 = 3.36694.


your 90% confidence interval is 33.03306 to 3.36694.