Question

Marvin lives in Stormwind City and works as an engineer in the city of Ironforge. In the morning, he has 3 transportation options (teleport, ride a dragon, or walk) to work, and in the evening he has the same 3 choicesfor his trip home. If Marvin randomly chooses his method of travel in the morning and in the evening, what is the probability that he teleports at least once per day?

Answer 1

The probability is 5/9.

The probability that he teleports at least once per day is the same as 1 - (probability he doesn't teleport).  The probability that he doesn't teleport in the morning is 2/3; in the evening it is 2/3.  This means the probability he doesn't teleport at all that day is (2/3)(2/3) = 4/9.  The probability he teleports at least once that day, then, is 1-4/9 = 5/9.