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STAT 200: Introduction to Statistics Final Examination, Spring 2016 OL1/US1 Page 2 of 7 1. True or False. Justify for full credit. (a) The standard deviation of a data set cannot be negative. (b) If P(A) = 0.4 , P(B) = 0.5, and A and B are disjoint, then P(A AND B) = 0.2. (c) The mean is always equal to the median for a normal distribution. (d) A 95% confidence interval is wider than a 98% confidence interval of the same parameter. (e) In a two-tailed test, the value of the test statistic is 1.5. If we know the test statistic follows a Student’s t-distribution with P(T < 1.5) = 0.98, then we fail to reject the null hypothesis at 0.05 level of significance . 2. Identify which of these types of sampling is used: cluster, convenience, simple random, systematic, or stratified. Justify for full credit. (a) A STAT 200 professor wants to estimate the study hours of his students. He teaches two sections, and plans on randomly selecting 10 students from the first section and 15 students from the second section. (b) A STAT 200 student is interested in the number of credit cards owned by college students. She surveyed all of her classmates to collect sample data. (c) The quality control department of a semiconductor manufacturing company tests every 100 th product from the assembly line. (d) On the day of the last presidential election, UMUC News Club organized an exit poll in which specific polling stations were randomly selected and all voters were surveyed as they left those polling stations. 3. The frequency distribution below shows the distribution for checkout time (in minutes) in UMUC MiniMart between 3:00 and 4:00 PM on a Friday afternoon. ( Show all work. Just the answer, without supporting work, will receive no credit.) Checkout Time (in minutes) Frequency Relative Frequency 1.0 - 1.9 3 2.0 - 2.9 12 3.0 - 3.9 0.20 4.0 - 4.9 3 5.0 -5.9 Total 25 (a) Complete the frequency table with frequency and relative frequency. Express the relative frequency to two decimal places. (b) What percentage of the checkout times was at least 4 minutes? (c) Does this distribution have positive skew or negative skew? Why?

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