Exam
Name___________________________________

MULTIPLE CHOICE.  Choose the one alternative that best completes the statement or answers the question.
Provide an appropriate response.
1) In an area of Russia, records were kept on the relationship between the rainfall (in inches) and the yield of wheat (bushels per acre). Construct a 95% confidence interval about the mean value of y, the yield, given  inches, and 
		1) _______

A) (43.56, 61.32)	B) (39.86, 65.98)	C) (49.41, 55.47)	D) (40.54 , 64.15)

2) In order for a company's employees to work at a foreign office, they must take a test in the language of the country where they plan to work. The data below shows the relationship between the number of years that employees have studied a particular language and the grades they received on the proficiency exam. Construct a 95% confidence interval about the mean value of y, given  and 
		2) _______

A) (58.28, 68.79)	B) (47.32, 72.13)	C) (51.50, 75.57)	D) (55.12, 87.34)

3) The data below are the temperatures on randomly chosen days during the summer and the number of employee absences at a local company on those days. Construct a 95% confidence interval about the mean value of y, the number of days absent, given x = 95 degrees,  = 0.449x - 30.27 and 
		3) _______

A) (6.345, 8.912)	B) (4.321, 6.913)	C) (11.336, 13.350)	D) (9.957, 14.813)

SHORT ANSWER.  Write the word or phrase that best completes each statement or answers the question.
4) A company keeps extensive records on its new salespeople on the premise that sales should increase with experience. A random sample of seven new salespeople produced the data on experience and sales shown in the table. Construct a 90% confidence interval about the mean value of y when x = 5 months.
		4)  _____________

1) C
2) A
3) C
4)  For x = 5,   = -0.25 + 1.315(5) = 6.325

 The confidence interval is of the form
 ± s

Confidence coefficient 0.90 = 1 - α ⇒ α = 1 - 0.90 = 0.10. α/2 = 0.10/2 = 0.05. From a Student's t table,  with n - 2 = 7 - 2 = 5 df. The confidence interval is
6.325 ± 2.015(1.577) ⇒ 6.325 ± 1.233 ⇒ (5.092, 7.558)