13. Public opinion polls are only estimates because (A) random digit dialing has replaced person-to-person interviewing. (B) all surveys have a sampling error. (D) samples of fewer than one million people are too small. (E) opinion polls have been deemed ineffective by political candidates.

(B) all surveys have a sampling error.

Step-by-step explanation:

1.4

2.3

step-by-step explanation:

the formula for the constant of variation is

y= kx

divide each side by x

y/x =kx/x

y/x =k

we know a and y

1.   y/x = k

4/1 =4

check the other values to make sure they are the same

8/2 = 4   12/3 =4   and 16/4 =4  

the constant of variation is 4

2.   y/x = k

3/1 =3

check the other values to make sure they are the same

6/2 = 3   9/3 =3   and 12/4 =3  

the constant of variation is 3

y=mx+b

step-by-step explanation:

m is slope, b is y-intercept