8.1

15

  1. Normal with xbar = 80, sd of x = 2

  2. .0668

  3. .0179

  4. .7969

17

  1. distribution must be normal - mu = 64, sd = 4.91

  2. .7486

  3. .4052

19

  1. .3520 = of randomly selected pregnancies would last less than 160

  2. normal sample distribution; mu of x = 266, sd of x = 3.58

  3. .0465

  4. .0040

  5. it would be highly unlikely this would happen with a populaion of 266 days - can assume our data would come from a population of with a mean of less than 266 days.

  6. .9844

21

  1. .3085

  2. .0418

  3. .0071

  4. increasing the sample size decreases the probability that x is greater than 95, because the more options you have, more will deviate toward the middle. more options leads to less room of error/variability. sd decreases as sample size grows.

  5. it is about as effective as the students were before. the probability that x is greater than 92.8 is .1056 which is not high enough to conclude that there is significant change.

  6. 97.3 wpm

23

  1. .5675

  2. .7291

  3. .8051

  4. .8531

  5. rate increases as investment time horizon increases - as we see adding a year increases each probability in b,c,&d.

8.2

11

  1. normal with a mean of .8 and sd of .05.

  2. .1922

  3. .0047

12

  1. normal with mean of .65 and a sd of .03

  2. .1894

  3. .0375

13

  1. normal with a sd of .02 and mean .35

  2. .0040

  3. .0233

14

  1. distribution is normal with a mu of p = .42 and a sd of .013

  2. .0102

  3. .0606

15

  1. qualitative - yes or no question

  2. random because it varies by sample; source is the individuals in a sample

  3. normal distribution with a mean of p = .47 and a sd of .035

  4. .1977

  5. .0239 - yes because only roughly 2% of samples of n=200 will result in less than 80 people being able to order in a foreign language.

16

  1. qualitative - answer is yes or no

  2. random becasue answer varies by sample and the source are the different individuals in each sample.

  3. normal with a mean of p=.82 and a sd of .038

  4. .2177 chance of it exceeding 85% happiness

  5. .0344 - yes only 3% of the time would 75 people or fewer are happy with things going on in their life.

17

  1. normal with a mu of p = .39 and a sd of .022

  2. .3288

  3. .3198

  4. .0838 - yes we expect only 40 of 500 adults per sample would say that marriage is obsolete.