Seventy percent of the students in a classroom are women and 30 percent are men. one student is described as ambitious, athletic, and assertive. why are most people likely to think this description refers to a male student?

The correct answer to this question is that:

People are “using the representativeness bias / heuristics”

In psychology, heuristics are rules or set of rules which people use to form judgements or decisions. In this case, people believe that an ambitious, athletic, and assertive person would be a representation of a male.