21.A university has 30,000 registered students. As part of a survey, 900 of these students are chosen at random. The average age of the sample students turns out to be 22.3 years, and the SD is 4.5 years. The average age of all 30,000 students is estimated as (i) . This estimate is likely to be off by (ii) or so. Fill in the blanks. (A) (i) 22.3 years (ii) 0.005 years (B) (i) 27.8 years (ii) 4.5 years (C) (i) 24 years (ii) 0.15 years (D) (i) 22.3 years (ii) 0.15 years 22. A survey is carried out at University of Texas at Dallas to estimate the percentage of undergraduates living at home during the current term. Nine hundred undergraduates are randomly picked. Among them, 150 are living at home. Compute a 95% condence interval for the proportion of undergraduates living at home. 1 (1/6)(5/6} 1 (1/6}(5/6) [A)Ei2* 150 (3)3i2* goo 1 (INKS/6) 1 (1/2)(1/2) [C] a i 2'58 * 900 (D) 3 i- 2 * goo 23. One opinion poll uses a simple random sample of 1,000 persons drawn from Town A with a population of 25,000 to estimate the proportion of Democrats. It turns out that 540 of the people in the sample are Democrats. The (i) proportion is 0.54- and its SE is (ii) . Fill in the blanks. m (A) sample, W (B) sample, V0.54 at 0.46 (C) population, % (D) population, V1000 * V0.54 at 0.46 24-. (Continuation) To estimate the proportion of Democrats, the poll uses a simple random sample of 1,000 persons from Town B with a population of 250,000. Which of the following is TRUE? (assuming others being equal) (A) The poll for Town A is likely to have higher SE than the poll for Town B. (B) The poll for Town B is likely to have higher SE than the poll for Town A. (C) The SE for the Town A and the SE for Town B are likelyto be similar. (D) We cannot tell which one has higher SE without the full data. 25. (Continuation) Another opinion poll uses a simple random sample of 16,000 persons drawn from Town A and a simple random sample of 4,000 persons from Town B to estimate the percentages. Assuming others being equal, the SE of the sample proportion for Town A is (A) about twice larger than the SE for Town B. (B) about four times larger than the SE for Town B. (C) about the same as SE for Town B. (D) about a half of SE for Town B. 26. (Bonus 1.) ln interval estimation, as the sample size becomes larger, the condence interval (A) becomes narrower. (B) becomes wider. (C) remains the same, because the mean is not changing. (D) gets closer to 2