Math Help - Dice

Hi, I am currently stuck on this extended response question from my book, I really don't know how to do the parts of the questions, could anyone help me? Thanks

You are given two un-biased dice, one painted red and one painted blue. You roll the dice and you record the numbers showing on each die. Let R by the random variable for the red die and B the corresponding random variable for the blue die.

(a) Write down the probability distribution for each of the random variables R and B.
(b) Write down the joint probability distribution, Pr(R,B). That is, the probability of obtaining, in the one roll, a specic value for R and a specic value for B.
(c) Use the joint distribution to deduce the probability distribution for R - B.
(d) Hence calculate the mean and standard deviation for R - B.

Originally Posted by usagi_killer

Hi, I am currently stuck on this extended response question from my book, I really don't know how to do the parts of the questions, could anyone help me? Thanks

You are given two un-biased dice, one painted red and one painted blue. You roll the dice and you record the numbers showing on each die. Let R by the random variable for the red die and B the corresponding random variable for the blue die.

(a) Write down the probability distribution for each of the random variables R and B.
(b) Write down the joint probability distribution, Pr(R,B). That is, the probability of obtaining, in the one roll, a specic value for R and a specic value for B.
(c) Use the joint distribution to deduce the probability distribution for R - B.
(d) Hence calculate the mean and standard deviation for R - B.

So what have you done? You should be able to do (a) and (b) straight off.

When you have done (b) for each point (r,b) in the sample space you have a probability, and you can compute r-b, then ...

CB

a)

b)

c)















d) Positive and negative factors are canceling, so