a)For a two-sided 100%*(1-alpha) confidence interval (CI), (alpha/2)100% probability falls above the upper limit, and (alpha/2)100% probability falls below the lower limit. For example, when the alpha level is .05, the certainty level of the CI becomes 95%, and .025+.025=.05 falls outside the CI. Later, we will call this alpha 'significance level' in the inference. If we want an 80% CI for an estimation, the alpha level becomes [X]. (write the answer as decimal; don't write as percent nor don't use the % symbol)

b)When the population standard deviation is not known, we use a t-distribution to get the critical value for a confidence interval. true of false

c)When calculating the critical value for a t confidence interval for one sample of size n, degrees of freedom we use is [X].

eSuppose a 95% confidence interval for the mean amount spent on a lunch is calculated to be ($9.90, $17.80). Which of the following is the correct interpretation (select the best choice)?

	A.	We are 95% confident that the interval ($9.90, $17.80) contains the population mean amount spent on lunch.
	B.	The true mean amount spent on lunch is between ($9.90, $17.80) with 95% certainty.
	C.	We know for almost certain that the true amount spent on lunch is between ($9.90, $17.80).
	D.	We are 95% confident that the interval ($9.90, $17.80) contains any sample mean amount spent on lunch.

fThe length of a two-sided confidence interval is 2*(Margin of Error). true false