Question

Past experience has indicated that the breaking strength of yarn used in manufacturing drapery material is normally distributed and that σ = 2 psi. A random sample of nine specimens is tested, and the average breaking strength is found to be 98 psi. Find a 95% two-sided confidence interval on the true mean breaking strength.

	A) 96.7 ≤ μ ≤99.3
	B) 87.8 ≤ μ ≤93.1
	C) 75.7 ≤ μ ≤83.0
	D) 97.6 ≤ μ ≤98.7

Question 12 (4 points)

a civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with σ ² = 1000(psi)². A random sample of 12 specimens has a mean compressive strength of x = 3250 psi. It is desired to estimate the compressive strength with an error that is less than 15 psi at 99% confidence. What sample size is required?

	A) 29
	B) 30
	C) 17
	D) 18

Cycling performance before and after an eight week leg-strength training was studied. Seven males performed leg-strength training three days per week for eight weeks. Peak power during incremental cycling increased to a mean of 315 watts with a standard deviation of 16 watts. Construct a 95% confidence interval for the mean peak power after training.

	A) [300.2, 329.8]
	B) [309.4, 320.6]
	C) [300.7, 329.3]
	D) [309.6, 320.4]

a particular brand of diet margarine was analyzed to determine the level of polyunsaturated fatty acid in percentages. A sample of six packages resulted in the following data: 16.8, 17.2, 17.4, 16.9, 16.5, 17.1. Calculate a 99% confidence interval on the mean.

	A) [16.501, 17.459]
	B) [16.455, 17.505]
	C) [16.540, 17.420]
	D) [16.497, 17,463]

A rivet is to be inserted into a hole. A random sample of n = 15 parts is selected, and the hole diameter is measured. The sample standard deviation of the hole diameter measurements is s = 0.008 millimeters. Construct a 99% lower confidence bound for σ2

	A) .024
	B) .000192
	C) .00384
	D) .000031

an article considered the use of EMS as a method to train healthy skeletal muscle. EMS sessions consisted of 30 contractions and were carried out three times per week for three weeks on 17 ice hockey players. The 10-meter skating performance test showed a standard deviation of 0.09 seconds. Construct a 95% confidence interval of the standard deviation of the skating performance test.

	A) [.067, .137]
	B) [.050, .208]
	C) [.005, .019]
	D) [.025, .043]

An article determined the essential amino acid Lysine composition level in soybean meal as shown below (g/kg):

22.2 24.7 20.9 26.0 27.0
24.8 26.5 23.8 25.6 23.9

Construct a 99% two-sided confidence interval for variance.

	A) [1.498, ∞]
	B) [1.520, ∞]
	C) [1.396, 19.038]
	D) [1.520, 20.138]

Answer 1