8.1
15
normal distribution with mean 80 and standard deviation 2
0.0668
0.0179
0.7969
17
The population must be normally distributed. If the population is normally distributed then the sample distribution is also normally distributed.
0.7486
0.3520
19
0.3520
Sampling distribution of x is normal with mean of 266 and standard deviation of about 3.578
0.0465
0.0040
Result is unusual so the sample probably came from a population that mean gestation period is less than 266 days
0.9844
21
0.3085
0.0418
0.0071
Increasing the sample size decreases the probability, because the standard deviation decreases as n increases
A mean reading rate of 92.8 wpm is not unusual.
5% chance that the mean reading rate of a random sample of 20 second grade students will exceed 93.7 wpm
23
0.5675
0.7291
0.8051
0.8531
Likelihood of earning a positive rate of return increases as the investment of time horizon increases
8.2
11
normal distribution with mean 0.8 and standard deviation 0.046
0.1922
0.0047
12
normal distribution with mean .65 and standard deviation .033
0.1867
0.375
13
normal distribution with mean .35 and standard devation 0.015
0.0040
0.0233
14
normal distribution with mean 0.42 and standard deviation 0.013
0.0102
-0.2843
15
Qualitative with two possible outcomes, order a meal or not
Source of the variability is the individuals in the survey and their ability to order a meal in a foreign language
normal distribution with mean .47 and standard deviation .035
0.1977
Yes it would be unusual because the probability is .0239 which means that about 2 out of 100 random samples of size n=200 Americans will result in 80 or fewer individuals which is unusual.
16
qualitative
the source of varibility are the americans asked whether they are satisfied or not
approximately normal
0.2418
yes
17
approximately normal
about 32 out of 100 random samples will result in less than 38% who believe marriage is obselete
(c)about 32 out of 100 random samples, will have between 40% and 45% where respondents believe marriage is obsolete