7. Large Sample Size. A researcher for a car deal- ership wants to estimate the

Question

7. Large Sample Size. A researcher for a car deal- ership wants to estimate the mean age of cars in his county. He goes to the largest shopping mall, he randomly selects 3,000 cars in the parking lot, and he obtains their ages from the registration stickers on the car win- dows. He then computes the mean age of the sample of 3,000 cars. The sample mean is a good estimate of the population mean, because the large sample size compensates for the fact that he is using a convenience sample. 0% the en- and and r the nake hese n 1s 8. Survey. In an Adecco Staffing survey of 1,000 con- have sam- esult mean adults in the United States, 140 (or 14%) said that salary was the most important feature of their job. The sample proportion of 0.14 cannot be a good estimate of the population proportion because this survey is based on such a small proportion of the population of adults.

Explanation / Answer

Ans:

7)sample size n=3000 is very large,so here,sample mean is good estimate of population mean.

Larger the sample size,estimate will be closer to the true value of population mean.

8)Rule of sample proportions:

n=1000

p=0.14

np=140>=10

here,sample proportion is good estimate of population proportion as np>=10

(sampel size should be 10% od poulation size)

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