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Econ 210 Winter 2009 First Midterm - Solutions

# Econ 210 Winter 2009 First Midterm - Solutions -...

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Northwestern University Department of Economics STAT 210 Introduction to Statistics - Professor: Steffen Habermalz First Midterm Examination – January 30 th 2009 INSTRUCTIONS : Please read the whole exam first. Questions are not ordered by difficulty. Answer all questions. Make sure you show ALL your work. Merely reporting the correct answer will not result in full credit. Write legibly. If we can’t read it, we won’t grade it. GOOD LUCK! 1. Write your name on the answer sheet. 2. (2+3=5 pts. each) True/False: State if the following statements are true or false. Only clearly explained answers earn full credit . a. The following is always true: P(C∩D 1 ) + P(C∩D 2 ) + P(C∩D 3 )=P(C) FALSE. While it looks like the law of total probability the statement is only true if the events D 1 -D 3 are exhaustive and disjoint. b. If E(X)=5 then E(X|Y)=5 FALSE. It’s the other way around. We know that due to the LIE we can write E(X)=E Y [E(X|Y)]. If E(X|Y)=5 this implies E(X)=5 but it is not true the other way around. c.

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Econ 210 Winter 2009 First Midterm - Solutions -...

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