To compare the effect of stress caused by noise on the ability to perform a simple task, 86 subjects were divided into two groups38 subjects as a control group, and 48 subjects as the experimental group. Although each subject performed the task, the experimental group had to perform the task while loud rock music was played. The time to finish the task was recorded for each subject and the following summary was obtained.

	Control	Experimental
n	38	48
x	17 minutes	24 minutes
s	5 minutes	11 minutes

(a)Find a 99% confidence interval for the difference in mean completion times (in minutes) for these two groups. (Calculate the difference as the control group the experimental group. Round your answers to two decimal places.) min to min(b)Based on the confidence interval in part (a), is there sufficient evidence to indicate a difference in the average time to completion for the two groups? Explain.The confidence interval in part (a) has ---Select--- two negative endpoints one positive and one negative endpoint two positive endpoints . Hence, it is ---Select--- plausible not likely that the means are equal. Based on the data we would conclude that ---Select--- there is there is no evidence of a real difference in the mean times to completion for the two groups.

2. ###

Independent random samples were selected from two quantitative populations, with sample sizes, means, and variances given below.

		Population
		1	2
Sample Size		36	46
Sample Mean		9.4	7.2
Sample Variance		8.56	14.52

Construct a 90% confidence interval for the difference in the population means. (Use

_{1 2}.

Round your answers to two decimal places.) to Construct a 99% confidence interval for the difference in the population means. (Round your answers to two decimal places.) to What does the phrase "90% confident" or "99% confident" mean?There is a 90% (or 99% as the case may be) chance that for any two samples, one sample from population 1 and one sample from population 2, the difference between sample means will fall within the interval. Hence, we are fairly certain that this particular interval contains _{1 2}.In repeated sampling, 90% (or 99% as the case may be) of all intervals constructed in this manner will enclose _{1 2}. Hence, we are fairly certain that this particular interval contains _{1 2}. In repeated sampling, 10% (or 1% as the case may be) of all intervals constructed in this manner will enclose _{1 2}. Hence, we are fairly certain that this particular interval contains _{1 2}.90% (or 99% as the case may be) of all values from populations 1 and 2 will fall within the interval. Hence, we are fairly certain that this particular interval contains _{1 2}.There is a 90% (or 99% as the case may be) probability that the interval will enclose _{1 2}. Hence, we are fairly certain that this particular interval contains _{1 2}.