venn diagram type probability: 42% of customers have internet service...

Suppose 42% of customers have internet service and 12.8% of customers have cable tv and internet service. Given that the customer has cable tv service, what is the probability of randomly selecting a customer that has internet service?

Ok so...

I thought the best way to do this would be to draw a Venn diagram.
I put P(of internet service)=43% in one circle.
I put P(of cable tv service)=57% in another circle.
I put P(of cable and internet)=12.8% in the intersection of the two circles.

So... do I need to find the intersection of P(of cable and internet) and P(Internet)? Is the answer just 12.8%? That can't be right...

I think I need to find the intersection of P(of cable and internet) and P(phone)? How do I do that? This type of question is driving me crazy.

Did you mean 42% or 43%? Which is right?

More important, are you told that every customer has either cable or internet? If not, I don't think there's enough information. Where does phone come in?

If everyone has cable or internet, then what you called 57% is not the probability of having cable; can you see what it is really?

Then, in order to answer the question, you'll have to know what conditional probability means. Were you given a formula or definition for P(A | B), in this case, P(internet | cable)?
 
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