8.1

15

  1. The curve is approximately normal with a mean of 80 and a standard deviation of 2.

  2. .0668 – out of a sample of 100, 7 would have mean higher than 83.

  3. .0179 – out of a sample of 100, about 2 would have a mean lower than 75.8.

  4. .7969 – out of a sample of 100, 79 would have mean between 78.3 and 85.1.

17

  1. The population must be normally distributed to compute probablitlies involving sample mean. the sample mean is 64 and the sample standard deviation is 4.907

  2. .7486 – in a random sample of 100, about 74 would have a mean less than 67.3

  3. .4052 – out of a random sample of 100, about 40 would have a sample mean less than 65.2.

19

  1. .3520 – out of 100 pregnanancies, about 35 are less than the average gestation period

  2. the mean is 266 days and the standard deviation is 3.57

  3. .0465– out of 100 randomly selected pregnancies, about 5 would be less than 260 days

  4. .0040 – out of 1000, about 4 would be less than 260 days

  5. the result is really rare so the sample probably came from a population whose mean gestation period was less than 66

  6. .9844 – out of a random sample of 100, about 98 would be between 256 and 276 21

  7. .3085

  8. .0418

  9. .0071

  10. Increasing the sample size decreases the probablity it occurs. the standard deviation decreases and n increases

  11. 92.8 is not unusual since the probability is .1056 . the new reasding program is not more affective than the old.

  12. there is a 5% chance that the mean reading speed of a random sample of 20 will exceed 93.7

23

  1. .5675

  2. .7291

  3. .8051

  4. .8531

  5. the likihood of earning positive rate increases as investment time horizion increases

8.2

11

  1. the sampling distribution is approx. normal, with an average of .8 and a standard deviation of .04618

  2. .1922 – about 19 out of 100 random sample size n=75 will result in 63 or more individuals with the characteristic

  3. .0047. about 5 in every thousand person

12

  1. this is approx a normal curve. mean= .65 standard deviation= .04

  2. .1867

  3. .0359

13

  1. curve is approx normal. mean = .35 and standard devation =.015

  2. .0035

  3. .0228

14

  1. Distribution approx normal. mean= .42 and standard deviation of .0129

  2. .0102

  3. .0606

15

  1. Qualititative because the answer is yes they can, or no they can’t. Not a number.

  2. The variability is whether they can order in a foreign language or not– some will be able to and some will not.

  3. its approx normal distribution with a mean = .47 and a standard deviation of .035

  4. .1949

  5. .0228– about 2 out of 100 random samle sizes of n=200 will result in 80 or fewer individuals who can order a meal in a foreign language

16

  1. The answer is qualitiative– its asking people for their opinion.

  2. The variability comes from whether people are satisfied or unsatisfied with the way things are going in their life.

  3. the distribution is approx. normal, sample mean= .82 and th standard deviation is .038

  4. .2148

  5. .0329– yes, it would be unusual

17

  1. the distribution is approx normal, the sample proportion mean= .39 ,the standard deviation = .022

  2. .3264

  3. .3231

  4. .0869