Edit Problem


I independent random variables
|
Easy


Fill in the rest of the joint distribution so that X and Y are independent. There are two possible answers:

Y X=0 1
0 ? 29
1 29 ?
Solution:

Let us consider the following probabilities:

  • P(X=0,Y=0)=a
  • P(X=1,Y=1)=b

From these, we can deduce:P(X=0)=a+29=P(Y=0)P(X=1)=29+b=P(Y=1)

Now, if we assume that X and Y are independent variables, then the joint probabilities can be expressed as the product of their individual probabilities. Therefore, we have:

P(X=0,Y=0)=P(X=0)P(Y=0)a=(a+29)2

Expanding and rearranging this equation, we obtain a quadratic equation:

a2+48159a=0

Solving this quadratic equation, we find that a can be either 19 or 49.

Similarly, for b, we have:

P(X=1,Y=1)=P(X=1)P(Y=1)b=(29+b)2

This simplifies to the same quadratic equation as for a, yielding the solutions b=19 or b=49.

Considering all possible combinations of a and b, we find the following two viable pairs that satisfy the independence requirement:

  • a=19,b=49
  • a=49,b=19

These pairs represent the solutions under the assumption of independence between X and Y.