# Graduate Statistics Final

1 . A numerical measure of a sample , is called a sample parameter

A ) True

B ) False

2 . A single numerical value used to estimate one particular value of the population is a point estimate

A ) True

B ) False

3 . A certain brand of electric bulbs has an average life of 300 hours with a standard deviation of 25 . A random sample of 64 bulbs is tested What is the probability that the sample mean will be less than 295

A ) 0 .0548

B ) 0 .1096

C ) 0 .4452

p D ) 0 .0793

E ) 0 .05 br

(z 0 .0793

4 . The standard deviation of a random variable is

A ) always positive

B ) always negative

C ) sometimes positive and sometimes negative

D ) depends on the mean of the random variable

E ) of the above

5 . The average advertising expenditure in the computer industry is found to be 15 ,000 ,000 annually , with a standard deviation of 3 ,000 ,000 . In a sample of 35 companies , what is the probability that the sample mean will exceed 16 million

A ) 0 .4756

B ) 0 .0244

C ) 0 .9544

D ) 0 .0456

E ) 0 .9756 br

(z 0 .4756

6 . In general , when the sample size stays the same , the higher the level of confidence , the narrower the confidence interval

A ) True

B ) False

7 . One way to get a narrower confidence interval is to increase the sample size

A ) True

B ) False

8 . As the level of confidence increases , the width of the confidence interval increases

A ) True

B ) False

9 . A survey of 49 people revealed that the mean number of minutes a person talks on the phone in one day in a particular locality is 26 with a standard deviation of 2 .5 . Give a 99 confidence interval for the average conversation time

A ) [25 .08 , 26 .92]

B ) [25 .14 , 26 .86]

C ) [25 .04 , 26 .96]

D ) [25 .17 , 26 .83]

E ) [25 .92 , 26 .92]

Solution : For 99 confidence interval , z 2 .575 10 . The mean of the sampling distribution of the sample mean is

A ) equal to the mean of the population

B ) an approximation of the mean of the population

C ) not a good estimate of the population mean

D ) equal to the population mean divided by n

E ) of the above

11 . The mean amount of money in the money market accounts of 36 customers is found to be 18 ,240 , with a standard deviation of 1 ,100 Construct of 99 confidence interval for the mean amount of money in the money market accounts at this bank

A ) [17813 , 18667]

B ) [17793 , 18687]

C ) [17768 , 18712]

D ) [17740 , 18740]

E ) [17151 , 19351]

Solution : For 99 confidence interval , z 2 .575 12 . When the sample size increases , everything else remaining the same the width of a confidence interval for a population parameter will

A ) increase

B ) decrease

C ) remain unchanged

D ) sometimes increase and sometimes decrease

E ) impossible to tell

13 . A tire manufacturer tests...

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