Chapter 6 Quiz - Confidence Intervals

1		A study was conducted to evaluate the stress level of senior business students at a particular college. Forty students were selected at random from the senior business class, and their stress level was monitored by attaching an electrode to the frontalis muscle (forehead). For the forty students, the mean EMG (electromyogram) activity was found to be 35.8 microvolts. In addition, the standard deviation of the EMG readings was found to be 2.5 microvolt. What would be the 99% confidence interval on the true mean EMG activity for all seniors in the class?
			A)	[34.2796, 36.8704]
			B)	[34.7296, 36.7804]
			C)	[34.9672, 36.7840]
			D)	[34.7456, 36.0566]
			E)	[34.9834, 36.5095]
2		For n = 121, sample mean = 96, and a known population standard deviation σ = 14, construct a 95% confidence interval for the population mean.
			A)	[93.53, 98.48]
			B)	[93.51, 98.49]
			C)	[93.02, 98.98]
			D)	[93.06, 98.94]
			E)	[93.00, 98.95]
3		The mean of the sampling distribution of the sample mean is:
			A)	equal to the mean of the population.
			B)	an approximation of the mean of the population.
			C)	not a good estimate of the population mean.
			D)	equal to the population mean divided by n.
			E)	none of the above.
4		For n = 25, sample mean = 645, and s = 55, construct a 99% confidence interval for the population mean.
			A)	[614.23, 675.77]
			B)	[617.59, 672.41]
			C)	[617.67, 672.34]
			D)	[613.43, 676.66]
			E)	[616.68, 673.33]
5		When the sample size increases, everything else remaining the same, the width of a confidence interval for a population parameter will:
			A)	increase
			B)	decrease
			C)	remain unchanged
			D)	sometimes increase and sometimes decrease
			E)	impossible to tell
6		A telephone company wants to estimate the mean number of minutes people in a city spend talking long distance with 95% confidence. From past records, an estimate of the standard deviation is 12 minutes. What is the minimum sample size required if the desired width of the confidence interval is 10 minutes?
			A)	28
			B)	11
			C)	23
			D)	19
			E)	42
7		In a department store, it is found that out of a randomly selected 64 customers, 21 buy cards. Construct a 95% confidence interval for the proportion of customers buying cards.
			A)	[0.3177, 0.3445]
			B)	[0.2316, 0.42471
			C)	[0.3214, 0.3349]
			D)	[0.2484, 0.5922]
			E)	[0.2131, 0.4432]
8		If the sample size is cut to 1/4 of its present size, all else being the same, the confidence interval will become:
			A)	twice as wide
			B)	half as wide
			C)	four times as wide
			D)	will not change
			E)	not enough information to determine
9		Suppose that in sampling for the population proportion, it is found that 20 out of 100 items are defective. Construct a 95% confidence interval for the proportion of defective items in the population.
			A)	[0.1216, 0.2784]
			B)	[0.0234, 0.3452]
			C)	[0.1212, 0.3341]
			D)	[0.175, 0.225]
			E)	none of the above
10		The management of a local restaurant wants to estimate the average amount their customers spend at the restaurant to within $0.50, with a 95% confidence. What is the minimum sample size required, if the standard deviation is assumed to be $3.50?
			A)	272
			B)	189
			C)	325
			D)	196
			E)	none of the above
11		A 95% confidence interval for ì is being formulated based on a sample of 16. What is the appropriate value for t?
			A)	1.746
			B)	2.120
			C)	2.131
			D)	2.473
			E)	2.490
12		A confidence interval for the population variance is being formulated, and a random sample of 35 observations yields a sample variance s2 = 2,120. What would interval limits for s2 be if a 95% confidence interval was desired?
			A)	1,483.1, 3,327.8
			B)	1,387.0, 3,638.6
			C)	1,308.4, 3,951.8
			D)	1,227.5, 4,368.5
			E)	1,167.5, 4,689.7