EBook Problems Estim Proportion

EBook Problems Set - Estimating a Population Proportion

Problem 1

A 1996 poll of 1,200 African American adults found that 708 think that the American dream has become impossible to achieve. The New Yorker magazine editors want to estimate the proportion of all African American adults who feel this way. Which of the following is an approximate 90% confidence interval for the proportion of all African American adults who feel this way?

• Choose one answer.

(a) (.56, .62)

(b) (.57, .61)

(c) Can't be calculated because the population size is too small.

(d) Can't be calculated because the sample size is too small.

Answer

 (b)

Problem 2

True or False: In a well-designed sample survey like the Current Population Survey, the observed sample percentage (e.g, percentage unemployed) is equal to the population percentage. Thus, it is appropriate to just report the sample percentage, without any measure of accuracy (i.e. without the margin of error).

• Choose one answer.

(a) True

(b) False

Answer

 (b)

Problem 3

The BBC news does a story and at one point the reporter says: "A polling agency reports that the percentage of the American public who agree we should spend more money on the mental health of the war veterans is 42% +/- 3%."

• Choose one answer.

(a) The probability that the American public agree that we should spend more money on the mental health of the war veterans is between 39% to 42%.

(b) The percentage of the American public who agree that we should spend more money on the mental health of the war veterans is between 39% to 45%.

(c) We are 95% confident that the percentage of the American public who agree that we should spend more money on the mental health of the war veterans is between 39% to 45%.

(d) The percentage of the American public who agree that we should spend more money on the mental health of the war veterans is 42%.

Answer

 (c)

Problem 3

A school district is worried that too many students are failing the high school exit exam. In a random sample of 60 high school students, there are 9 students who fail the exit exam. Administrators want to estimate the percentage of the students who fail with a margin of error of 3% and confidence level of 90%. How many students should they sample for a thorough investigation of the problem?

• Choose one answer.

(a) 278

(b) 544

(c) 383

(d) 233

Answer

 (c)

Problem 4

A major newspaper wants to hire a polling agency to predict who will be the next governor. Agency A proposes to do the job with a random sample of 5000 voters at a cost of $50K (K = one thousand). Agency B proposes to do the job with a random sample of 7500 voters at a cost of $75K. Assume both agencies find the percentage of voters to be 40% and both use the normal model to calculate the 95% interval. Which agency will you hire? Hint: Compare the margin of error for the two agencies and the relative costs before making your decision.

• Choose one answer.

(a) I will hire B.

(b) I have no preference.

(c) I need more information to decide who to hire.

(d) I will hire A.

Answer

 (d)

Problem 5

Suppose that the proportion of the adult population who jog is 0.15. What is the probability that the proportion of joggers in a random sample of size n =200 lies between 0.13 and 0.17?

• Choose one answer.

(a) 0.5762 approximately

(b) 0.8125 approximately

(c) 0.2345 approximately

(d) 0.1234 approximately

Answer

 (a)

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