Probability question conditional

You are lost in the National Park. Tourists (which look just like indians) comprise two-thirds of the visitors to the park, and give a correct answer to requests for directions with probability 3/4. (Answers to repeated questions are independent, even if the question and the person are the same.) If you ask an indian for directions, the answer is always incorrect.


(a) You ask a passerby whether the exit from the Park is East or West. The answer is East.


What is the probability that this is correct?
(2/3)(3/4) + (1/3)(0) = 1/2




(b) You ask the same person again, and receive the same reply. What is the probability of being


correct?


(2/3)(3/4)^2+(1/3)(0)^2
i think




(c) You ask the same person for the third time, and receive the same reply. What is the probability


of being correct?

(2/3)(3/4)^3+(1/3)(0)^3
?


(d) You ask for the fourth time, and receive the same reply. What is the probability of being
correct?

(2/3)(3/4)^4+(1/3)(0)^4


(e) Had the fourth answer been West instead, what is the probability of East being correct?

(2/3)(3/4)^4+(1/3)(0)


(f) Contrast your answers in part d and part e and explain.
They are the same?

I would have thought we were beyond racist questions by now!

Your answer to "E" is incorrect. Since are told that "Indians always answer incorrectly", the fact that you get a different answer means that this person must be a tourist. the probability he is a tourist is now 1, not 2/3.

I certainly hope the teacher that made up this problem was fired.