6.1 a & c
    f is a pdf if and only if 1)f>=0 2)Area under f is 1.

6.6 .3

6.9 Z=(X-15)/4, Z=(X-61)/9, Z=(X-161)/5

6.12 .8830 ; .5714

6.15 .2033; .0023; .8907; 

6.29 .0668; .0062; .9198

6.34 .0179; .1587^2=.0252;  .0179

6.48 no (if np>15 & nq>15, then normal will be a fairly good 
        approximation, here the condition is not satisfied.)


7.2 a. stat:# of movies received the distinction of generating the most box office revenue for a weekend
       population:movies shown in the first half of 2003
    b. stat: proportion of minority living in Chicago.
       population:minority living in Chicago
    c. stat: proportion of labrador retriever among dogs having licences in northern wisc
       population:dogs having licences in northern wisc

7.3 a. stdts having evening class have higher chance to work part time.
    b. seasonal change

7.5 b. X*  f(x*)
       3   1/9
       4   2/9
       5   1/3
       6   2/9
       7   1/9

7.13 4 2 1

7.17 a).04, .24, .04
     b)2
     c)2 & .0111

7.26 .0548