1. Answers to Assign. 19-3: Ch. 19 Practice1)
Condition
Check
Random Sample
We have to assume this
n < 10% of N
We know 1500 is <10% of all Americans
np ≥ 10 and n(1 – p) ≥ 10
(we have to use p instead)
1500(.68) ≥ 10
1020 ≥ 10
1500(.32) ≥ 10
480 ≥ 10
We are 97% confident that between 65.4% and 70.6% of all Americans support campaign finance reform. ^

2. 2)
Condition
Check
Random Sample
We have to assume this
n < 10% of N
We know 200 IS < 10% of all HS seniors
np ≥ 10 and n(1 – p) ≥ 10
(we have to use p instead)
200(.74) ≥ 10
148 ≥ 10
200(.26) ≥ 10
52 ≥ 10
We are 99% confident that between 66.0% and 82.0% of all high school seniors feel that their high school experience has been valuable. ^ 2

3. 3) Yes, the interval we calculated supports his belief since 70% falls within it.4)
Condition
Check
Random Sample
Assume
n < 10% of N
We know 1039 is <10% of all adults
np ≥ 10 and n(1 – p) ≥ 10
(we have to use p instead)
1039(.39) ≥ 10
405 ≥ 10
1039(.61) ≥ 10
634 ≥ 10
We are 95% confident that the true proportion of adults who plan to take more vacations this year is between 36.0% and 41.9%. ^ 3

4. 5) 6)