If X & Y are the times that each of the two friends arrive, then you want the probability that . Look at the graph. What is the probability that the random point (X,Y) is between the two blue lines?

Now, I have a word of caution for you. You have had a great many of these problems, probably take-home problems, worked for you. If you are doing any of this online you need to read my posting about online courses.

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