Probability / Conditional Probability: If 2 fair dice rolled, what is cond. prob...?

[markeca]

Hi! Lately, I am confuse and having difficulty with conditional probability. So if you could help me, it would really be a great help. Thank you.

If two fair dice are rolled, what is the conditional probability that the first one lands on 4 given that the sum of the dice is k? Compute for all values of k between 5 and 10.

 

[HallsofIvy]

In order that the sum be "k", if one lands on a "4" then the other must land on "k- 4".

If k= 5, k- 4= 1. What is the probability a die lands on "1"?
If k= 6, k- 4= 2. What is the probability a die lands on "2"?
If k= 7, k- 4= 3. What is the probability a die lands on "3"?
If k= 8, k- 4= 4. What is the probability a die lands on "4"?
If k= 9, k- 4= 5. What is the probability a die lands on "5"?
If k= 10, k- 4= 6. What is the probability a die lands on "6"?

 

[markeca]

Thank you for replying. I somehow get it now. Do I just have to get the probability if one lands on 1,2,3,4,5,6? Or do I also have to get the conditional probability which is in the question? If I have to, then how do I solve for it?

 

[HallsofIvy]

You say "I get it now" but you questions indicate you do not even understand what the question is asking. Do you understand what "conditional probability" means? It is "the probability if one lands on 1,2,3,4,5,6". Your two options are the same.