Spring2011Exam2Solutions

Spring2011Exam2Solutions - STAT 225 Spring 2011 Exam 2...

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STAT 225 – Spring 2011 Exam 2 – ANSWER KEY Your Name: ___________________________________________ Your Section: Zhaonan (7:30) Zhaonan(8:30) Jeff (9:30) Jeff (10:30) Mike (11:30) Chris (12:30) Yen-Ning (1:30) Yen-Ning (2:30) Lin-Yang(2:30) Yong (3:30) Jeremy (3:30) Jeremy (4:30) Note: Show your work on ALL questions. Unsupported work will NOT receive full credit. All answers should be in decimal form and should be exact, or to at least taken out to two decimal places or two significant figures . You are responsible for upholding the Honor Code of Purdue University. This includes protecting your work from other students. Please write legibly . If a grader can not read your writing, NO credit will be given. You are allowed the following aids: a one-page 8 ½” x 11” handwritten (in your handwriting) cheat sheet, a scientific calculator, pencils and erasers. You may be asked to show your student ID (upon request) and turn in your cheat sheet when you turn in your exam to your instructor. Turn off your cell phone before the exam begins! Question Points Possible Points Received 1 18 2 12 3 11 4 10 5 12 6 13 7 13 8 10 Cheat Sheet 1 Total 100
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1 1. A STAT course has 400 students in the spring semester. The instructor is trying to do some estimation about the course using information from previous semesters. In each of the following situations, there is a random variable involved. Find its PMF by name and parameter(s). If an approximation can be made, you must name and label both the exact and approximate distribution with corresponding parameter(s) to receive full credit. (3 points each) a). It is known that 70% of all students will complete all the old exams and review problems as they prepare for the exams. Let A represent the number of students in this course in spring semester who complete all the review materials. A~BIN(400, 0.7) b). Usually 1.2% of all students choose not to use a cheat sheet on the exams. Let B represent the number of students in this course in spring semester who do NOT use cheat sheet on the exams. Exact: B~BIN(400, 1.2%) c). It is known that 35% of all students own a graphing calculator. We randomly select a group of 50 different students. Let C represent the number of students among the 50 selected ones who do NOT own a graphing calculator. C~HG(400, 50, 0.65) or C~HG(400, 50, 260) d). 20 students in this course have reported that they have schedule conflicts with the scheduled exam. We randomly select a group of 15 students. Let D represent the number of selected students who have schedule conflicts with the scheduled exam. Exact: D~HG(400, 15, 20 or 0.05) Approx: D~BIN(15, 0.05) e). Every semester, there is a course-wide lottery which randomly selects 1% of all students to receive a free pass in this course without having to do any work. Let E represent the outcome that a student gets a free pass. E~Bernoulli(0.01)
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Spring2011Exam2Solutions - STAT 225 Spring 2011 Exam 2...

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