7 .Scenario: Concrete Strength . An engineer wants toknow if the strength of two

A) b) Two-sample t-testof the mean. B) a) mu(1)– mu(2) =0, mu(1)– mu(2).ne. 0 C) d) 2.306 D) c) -3.80 E) b) (-1307, -321) F) a) Yes

ID: 2952347 • Letter: 7

Question

7.Scenario: Concrete Strength.

An engineer wants toknow if the strength of two separate concrete mixes aredifferent.

He randomly selects 9cylinders of mixture 67-0-301 (sample #1) and 10 cylindersof

mixture 67-0-400(sample #2). After 28 days, he measures the strength (in poundsper

square inch) of the 6by 12 inch cylinders and obtains the information below.Use

significance level0.05.

Boxplot = all pointsinside fences.

Normal probabilityplot = all points inside bounds.

Sample # n x s

67-0-301 1 9 3,669 458.5

A. What is theappropriate test procedure? ____ (4 pts)

a) Two-samplez-test of the mean. b) Two-samplet-test of the mean.

B. What is theappropriate set of hypotheses(H0, H1)? ____ (3 pts)

a)mu(1) – mu(2) =0, mu(1)– mu(2).ne. 0

b)mu(1) – mu(2).ne. 0, mu(1)– mu(2) =0

c)mu(1) – mu(2) =0, mu(1)– mu(2)< 0

C. What is the correctmagnitude of the critical value? ____ (3 pts)

a) 2.110 b)2.093

D. What is the correctvalue of the test statistic? ____ (3 pts)

a) 1.96 b)+3.80

E. What is the correctconfidence interval? ____ (3 pts)

a) (-904, -473) b)(-1307, -321)

F. Are these concretemixes significantly different in strength? ____ (4 pts)

a) Yes. b)No.

c) Sometimes. d) Maybe.

A) b) Two-sample t-testof the mean. B) a) mu(1)– mu(2) =0, mu(1)– mu(2).ne. 0 C) d) 2.306 D) c) -3.80 E) b) (-1307, -321) F) a) Yes

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