8.1

15

  1. μ = 80, x = 2̅.

  2. .067.

  3. .018.

  4. 80%.

17

  1. 4.907

  2. .748.

  3. .405.

19

  1. 0.3557, 36% of pregnancies will last less than 260 days.

  2. 3.58.

  3. 0.046.

  4. 0.0040.

  5. It would be unsual and the mean would probubly be less than 266.

  6. .9845.

21

  1. the probability is 30.9.

  2. 0.418.

  3. .0071.

  4. as the sample size increases the probabiity decreases that it will be 95 or higher because the more samples the more it wants to be closer to the mean.

  5. it is not unsusal because it is .1046.

  6. .5% chance that the mean reading speed of a random sample of 20 second grade students would exceed 93.7

23

  1. .5675.

  2. .727, about 73 of the monthly rates will be positive.

  3. .805, 81 of samples will be postive.

  4. .8531, 85 will be postive .

  5. The likelyhood of earining a positive rate of return increases as investment time horizon increases.

8.2

11

  1. .0462.

  2. .193.

  3. .0045.

12

  1. .0337.

  2. .187.

  3. .038.

13

  1. .015.

  2. .0040.

  3. .023.

14

  1. .013

  2. .0105.

  3. .062.

15

  1. qualitative.

  2. varibil.ity in the people being survayed.

  3. .035.

  5. .023, unusual.

16

  1. qualtitative

  2. its randomly selectided people.

  3. .038.

  4. .215.

  5. yes, it is unusual because .0327.

17

  1. .022.

  2. .2338.

  3. .3215

  4. .0863.