EECS 126 Fall 2001 Midterm 1 Exam Questions, Exams of Probability and Statistics

The questions from midterm 1 exam of eecs 126 fall 2001. The exam consists of five problems covering topics such as probability theory, random variables, and conditional distributions. Students are required to determine if given statements are true or false and provide explanations for their answers. The document also includes problems on finding conditional distributions and expected values.

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2012/2013

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<!--EECS126, exam #1, Fall/2001 -->
*EECS 126 Fall 2001
Midterm 1
The exam starts at 3:40 p.m. sharp and ends at 5:00 p.m. sharp.
There are 5 problems. The maximum score is 50 points.
The exam is open book open notes.
Problem #1
For each of the following statements, indicate whether you believe that the statement is
true or believe it is false, and give a briefs explanation of your reasoning. A correct answer
without a valid explanation gets 1 points. A correct answer with a valid explanation gets 3 points.
(a) For any three events A, B, and C, if P (A B) > 0 and P(B C) > 0,
then P (A C) > 0.
(b) Given two events A and B with P(A) > 0 and P(B) > 0 , if P( A | B) > P(A) then P
(B|A) > P(B).
(c) Two card are drawn at random without replacement from as standard deck of 52
playing cards
(i.e. the first card is drawn at random and then the second card is drawn at random
from the remaining cards.)
Then the event that the two cards are both aces is independent of the event that they
are both diamonds.
(d) g(x) is a real valued function on R satisfying g(x) >= x. Let X be a random variable
and let Y = g(X).
The FY(z) <= FX(z) for all z R.
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*EECS 126 Fall 2001

Midterm 1

The exam starts at 3:40 p.m. sharp and ends at 5:00 p.m. sharp. There are 5 problems. The maximum score is 50 points. The exam is open book open notes.

Problem #

For each of the following statements, indicate whether you believe that the statement is true or believe it is false, and give a briefs explanation of your reasoning. A correct answer without a valid explanation gets 1 points. A correct answer with a valid explanation gets 3 points.

(a) For any three events A, B, and C, if P (A B) > 0 and P(B C) > 0, then P (A C) > 0.

(b) Given two events A and B with P(A) > 0 and P(B) > 0 , if P( A | B) > P(A) then P (B|A) > P(B).

(c) Two card are drawn at random without replacement from as standard deck of 52 playing cards (i.e. the first card is drawn at random and then the second card is drawn at random from the remaining cards.) Then the event that the two cards are both aces is independent of the event that they are both diamonds.

(d) g(x) is a real valued function on R satisfying g(x) >= x. Let X be a random variable and let Y = g(X). The FY(z) <= FX(z) for all z R.

(e) Adding a constant to a random variable does not change its standard deviation.

(f) A random variable X is known to satisfy FX(-2) = 0 and F (^) X(10) = 1. Then it must have finite variance.

(g) If X is a random variable and Y = X 1/3, then the characteristic function of Y can be determined from the characteristic function of X.

Problem #

7 points.

Consider the array of 25 points

{(i , j) : 1 <= i <= 5, 1 <= j <= 5}

Choose a point at random from among these. Call this point Aa. Choose another point at random from

among these, independently of the choice of the first point. Call this point Qb.

Let B denote the event that the points A (^) a and Qb are either in the same row or in the same column. This includes the possibility that Qa = Q (^) b. Another way to describe B is that it is the event where Qa

and Qb

have either the same first coordinate of the same second coordinate (or both , i.e. they are the same point).

What is the conditional distribution of Q (^) a among the 25 pints, conditioned on B?

Problem #3.

5 points.