1
SOC 360
Practice Exam 2 Answer Key
Part I True/false
1. False
2. False
3. True
4. True
5. True
6. False
Part II. Multiple Choice
7. B
13. A
8. D
14. E
9. A
15. A
10. C
16. A
11. G
12. B
Part III.
17. SD = 100/ 20 = 22.36
B. normal distribution.
C. P( x > 560) = P(Z > (560-500)/22.36) = P(Z > 2.68) = 1-0.9963 = 0.0037
18. A. Let X be the annual return of stocks, P(X < 0) = P(Z < (0-10)/26) = P(Z < -0.385)
= 0.3483 (0.3520 is OK too)
B. SD = 26 / 45 = 3.88 (%)
C. P(X < 0) = P(Z < (0-10)/3.88) = P(Z < -2.58) = 0.0049
D. The probability of a loss in the long term is much smaller than that in the short term
(0.0049 vs. 0.3483)
19A. z* = 1.645
19B. z* = 2.807
20A. SD = 2000 / 325 = 110.94
20B. a 98% CI: 6200 ± 2.326*(110.94) = 6200 ± 258.05 = (5942, 6458)
20C. ± 258 (258 OK)
21A. x = 107.8, a 96% CI: 107.8 ± 2.054* (15/ 10 ) = 107.8 ± 9.74 = (98.06, 117.54)
21B. No, we cannot reject H0 because 100 is within the 96% CI. There is no significant
evidence that mean IQ scores in the population differs from 100 at α = 0.04 level.
2
22A SD = 35/ 25 = 7
22B Note: the center of density curve is 120, 95% of area is between 106 and 134.
(shape: normal; mean = 120; pay attention to the width when you draw the curve.)
22C The test is two-tailed, so the area to the right of 130 and to the left of 110 is shaded.
23A H0: µ = 7.5
Ha: µ < 7.5
7 − 7 .5
23B. z =
= -1.414
2.5 / 50
23C. (z < -1.414) = 0.0793
23D. cannot reject H0.
24A. H0: µ = 12
Ha: µ ≠ 12
12.9 − 12
24B. z =
=3
3 / 100
24C. P(z >3) = 1-0.9987 = 0.0013, p-value = 2* 0.0013 = 0.0026
24D. Reject H0, very good evidence against the politician’s claim.
25A. a 95% CI: 8.6 ± 1.96*(
3 .2
) = 8.6 ± 0.3626 = (8.24, 8.96)
300
25B. n = (1.96*3.2/0.1)2 = 3933.8, we take n = 3934
26A. All faculty of Occidental University
26B. Stratified Random Sampling
26C. Undercoverage.
27. Larger sample size for women than men.