8.1

15

  1. It is approximately normal with u=80 and o=2

  2. .0668, if we take 100 random samples, 7 of them will result in a mean that is greater than 83.

  3. .0179, if we take 100 random samples, about 2 of them will result in a mean that is less than or equal to 75.8.

  4. .7969, if we take 100 random samples, then about 80 of them will result in a mean that is between 78.3 and 85.1.

17

  1. The population must be normally distributed to compute probabilities involving the sample mean. If the population is normally distributed, then the sampling distribution of x is also normally distributed with u=64 and o=4.907

  2. .7486. 75 of the 100 samples will result in a mean that is less than 67.3.

  3. .4052. 40 or 41 of the 100 samples will result in a mean that is greater than or equal to 65.2.

19

  1. .3520, 35 of the 100 human pregnancies will last less than 260 days.

  2. the sampling distribution of x is normal

  3. .0465, 5 of the 100 random samples will result in a mean gestation period of 260 days or less.

  4. .0040, 4 of the 1000 samples will result in a mean gestation period of 260 days or less.

  5. This result would be unusual, so the sample probably came from a population whose mean gestation period is less than 266 days.

  6. .9844, 98 of the 100 samples will result in a mean gestation period between 257 and 276 days, inclusive.

21

  1. .3085, 31 of the 100 students will read more than 95 words per minute.

  2. .0418, 4 of the 100 samples will result in a mean reading rate that is more than 95 words per minute.

  3. .0071, 7 of the 1000 samples will result in a mean reading rate that is more than 95 words per minute.

  4. increasing the sample size decreses P(x>95). This happens because decreases as n increases.

  5. A mean reading rate of 92.8 wpm is not unusual since P(x>=92.8). This means that the new reading program is not abundantly more effective than the old program.

  6. 93.7 words per minute

23

  1. .5675

  2. .7291

  3. .8051

  4. .8531

  5. The likelihood of earning a positive rate of return increases as the investment time horizon increases.

8.2

11

  1. approximately normal

  2. .1922

  3. .0047

12

  1. Type answer here.

  2. Type answer here.

  3. Type answer here.

13

  1. approximately normal

  2. .0040

  3. .0233

14

  1. Type answer here.

  2. Type answer here.

  3. Type answer here.

15

  1. qualitative with 2 possible outcomes- order a meal in a foreign language, or not.

  2. The source of the variability is the individuals in the survey and their ability to order a meal in a foreign language.

  3. It is approximately normal with with u=.47 and o=.035

  4. .1977

  5. .0239, this is unusual because only 2 out of 100 random samples of size n=200 Americans Americans will result in 80 or fewer individuals who can order a mwal in a foreign language.

16

  1. Type answer here.

  2. Type answer here.

  3. Type answer here.

  4. Type answer here.

  5. Type answer here.

17

  1. approximately normal with u=.39 and o=.022

  2. .3228

  3. .3198

  4. .0838, this result is not unsual.