Thomas has devised a scheme for splitting up the test and training set. For each row from coordinates: Rows for Stanford students have a 50% chance of being placed in the train set and 50% chance of placed in the test set. Rows for Berkeley students have a 80% chance of being placed in the train set and 20% chance of placed in the test set. Given that a row is in the test set, what is the probability that it corresponds to a Stanford student? Assign that probability to prob_furd.