Each month the census bureau mails survey forms to 250,000 households asking questions about the people living in the household and about such things as motor vehicles and housing costs. telephone calls are made to households that don't return the form. in one month, responses were obtained from 240,000 of the households contacted.. reference: ref 7-1. the sample is. a. the 250,000 households initially contacted.. b. the 240,000 households that respond.. c. the 10,000 households that did not respond.. d. all u. s. households.

solution:

the given function is ,

      =

the three roots of this quadratic function is , 0 ,8 and 10.all the roots are real and rational.

if a quadratic equation is of the form ,

sum of the roots = a + b +c= 0+8+10=18=  

product of roots taken two at a time = a b + b c+ c a = 0+80+0=80 =  

product of roots = a b c = 0=  

there are 11 doors in a hall starting from 0 to 11.the entry in the hall is permitted through gate number 0 and exit is allowed through only gate number 8 and 10.so, three roots(0,8,10) of quadratic function is given by entry and exit route of this hall.

b, i believe, but not sure.