# Thread: Tabulating probabilities of dependant r.v

1. ## Tabulating probabilities of dependant r.v

Hi, I've got a question but before I can get going I need to tabulate the probabilities and am coming unstuck early on...

Q:
Finding 4 coins in his pocket, Al proposes a game of chance. He will toss all 4 coins; let X denote the number of heads obtained. Penny will then toss all the coins which came up tails when Al tossed them. Let Y denote the number of heads Penny obtains.
What formula would I use to find the joint probability? Is it conditional as Y is dependant on X?
Maybe someone could help with this ( for example X = 4 Tails and Y= 4 Tails or some other so I can get the idea...)
Dojo

Thanks

2. Originally Posted by dojo
Hi, I've got a question but before I can get going I need to tabulate the probabilities and am coming unstuck early on...

Q:
Finding 4 coins in his pocket, Al proposes a game of chance. He will toss all 4 coins; let X denote the number of heads obtained. Penny will then toss all the coins which came up tails when Al tossed them. Let Y denote the number of heads Penny obtains.
What formula would I use to find the joint probability? Is it conditional as Y is dependant on X?
Maybe someone could help with this ( for example X = 4 Tails and Y= 4 Tails or some other so I can get the idea...)
Dojo

Thanks
You will have a 5x5 grid with X at the top and Y on the side. Each cell in the grid is of the form (x, y). Fill in the values in each of the cells according to the rule you were given:

"He will toss all 4 coins; let X denote the number of heads obtained. Penny will then toss all the coins which came up tails when Al tossed them. Let Y denote the number of heads Penny obtains."

3. I dont know what rule to use. That is the problem...