When Mandy and Joe meet, Joe tells her that he loves math and computers and his favorite hobbies have always involved building things. Mandy concludes that Joe must be an engineering student rather than a liberal arts student, even though there are many more liberal arts than engineering students at their school. Mandy is using the heuristic and ignoring .

Representativeness , base rates

Explanation:

Representativeness heuristic is defined as observing similarity among the things or events and then categorizing it as per its prototype.This eases the process of making judgement as per probability based on certainty shown classification of objects through mind shortcut.

Base rates are the statistical percentage that determine about population persisting particulate trait.This probability does not involved information about other traits.

According to the question, Mandy is basing her decision on representativeness heuristic as she is going along with the probability created by mental shortcut as per category prototype i.e- engineering student and liberal arts students.She is ignoring base rates as it has certain characteristic based probability.