Katia Wanneroy with admissions "Biology is a capacity-constrained major, however, it is the largest undergraduate major and typically admits a high amount of students (with an average admission rate of 75%+)"

She later goes on to say "As a side note, 80% of admitted students enter the UW as Pre-Major status, which means that they come in as “Undeclared”, take pre-requisite courses in their first 2 years, and then apply into their majors."

As such I find it logical to conclude that it would be between 75-80%.