Please give the original problem statement. You haven't posted enough of the problem for us to figure it out.
It is remarkable not much different than what you see now.
What is the probability that it occurred:
In a rural area, given that the speed limit was no more than 40mph?
There is a chart as well but I am simplifying trying to figure out if that is saying rural intersect with under 40mph as the set in question.
OK, I'm going to stick my neck out and guess that your question is:
What is the probability that a car accident will occur in a rural area, given that the speed limit is no more than 40 mph.
Correct?
It's hard to know how to answer this without knowing more about your chart. What does it look like?
[edit]Changed "under" to "no more than" above.[/edit]
I'm still trying to guess your original question. OK, let's try again. I'm guessing the question is "If an accident occurs in an area where the speed limit is not more than 40 mph, what is the probability that it is in a rural area?"
Proceeding symbolically, let
R be the event that the accident occurs in a rural area and
L be the event that the speed limit is less than or equal to 40 mph
Then I think the probability you want is
by the definition of conditional probability.
Do you see how to find the numbers you need in your chart?
[edit]It's getting late here, I'm going to have to sign off soon[/edit]