Marginal/Conditional Probability Mass Functions

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SUMMARY

The discussion centers on calculating the marginal and conditional probability mass functions (pmf) for a scenario involving four dice, each labeled from 1 to 4. The marginal pmf for X, representing the die chosen, is uniformly distributed with Px(x) = 1/4 for x = 1, 2, 3, 4. The conditional pmf for Y, which indicates the color of the face showing (0 for black, 1 for white), is derived based on the number of white faces on each die. For example, Pr(Y=0|X=1) = 5/24 and Pr(Y=1|X=1) = 1/24, with similar calculations for other values of X.

PREREQUISITES
  • Understanding of probability mass functions (pmf)
  • Familiarity with conditional probability concepts
  • Basic knowledge of combinatorial counting principles
  • Ability to construct and interpret probability tables
NEXT STEPS
  • Study the derivation of marginal pmf for discrete random variables
  • Learn how to compute conditional probabilities using Bayes' theorem
  • Explore examples of probability distributions in real-world scenarios
  • Practice constructing 2D probability tables for joint distributions
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vikkisut88
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Homework Statement


A bag contains four dice labelled 1,...,4. The die labelled j has j white faces and (6-j) black faces, j = 1,...,4. A die is chosen at random from the bag and rolled. We define X = the number labelling the chosen die.
Y = {0 if the face showing on the die is black; 1 if the face showing on the die is white.

Construct a table displaying the values of the marginal pmf (probability mass function) for X and a separate table displaying the values of the conditional pmf for Y fiven X=x for general x.

Homework Equations


Marginal pmf for X is Px(x) = P(X=x) = \sum P(x,y)
Conditional pmf for Y given X=x is PY/X(y,x) = P(x,y)/Px(x)

The Attempt at a Solution


Okay so i know the two equations above for the two pmf's. I'm presuming that for the first part (marginal pmf) that you just use x=1,2,3,4 and that Px(x) is 1/4 for each value of x?
For the second table I'm not so sure as I don't know which y values to put into my table, and how to work out any probabilities as it has to be for a general x and not a given value of x. As at the beginning of the question it states that y=0 or y=1 is it just these two values that i put into my table n then depending on when x=1,...,4 will alter the probability
 
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vikkisut88 said:
as it has to be for a general x and not a given value of x
I think they're asking for a 2D table, so for each x you have a distribution for y.
 
X=1, then Pr(Y=0|X = 1)=5/24, Pr(Y=1|X=1)=1/24;
X=2, then Pr(Y=0|X=2)=4/24, Pr(Y=1|X=2)=2/24;
Continue for each value of X.
 

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