Ch. 7 REVIEW PROBLEMS 231 



Ans. ix ^59.7; a ^ 21.9. 



7. Construct an r.c.f. curve for the data of problem 6 and obtain from it evi- 

 dence regarding the normality of the distribution of these test scores. 



8. In what percentile would a person who made a score of 101 rank in the 

 test of problem 6? Ans. 97th. 



9. What are the modal and the median test scores, respectively, for prob- 

 lem 6? 



10. Calculate the median for the Ohio test scores of problem 6 by grouping 

 them into about 12 classes of equal length. Ans. md ^51 .6. 



11. The Year Book of Labour Statistics for 1943-1944 gives the following per- 

 centages of unemployed in the United States and Sweden during 1941, by 

 monthly averages: 



In which country was the level of unemployment relatively more stable during 

 that year? Justify answer statistically. 



12. The USDA publication, Agricultural Statistics, 1946, lists the following 

 tax levies for the 48 states, in dollars per acre: 



Compute the median tax per acre from an array of these data. Also compute 

 the range and the midrange. Compare the latter with the median and draw 

 any possible conclusions. Ans. md = 40; range = 2.69; MR = 1.38. 



13. Referring to the data of problem 12, in what decile would a state rank 

 if its tax rate were 0.40 dollars per acre? What percentage of the states would 

 have a higher rate? 



14. Suppose that a sample of 15 differences in yield between two varieties of 

 corn grown side by side on 15 pairs of plots has been found to have an arithmetic 



