Sarah's grade was 50th percentile of the 20 grades for her class

Sarah's grade was 50th percentile of the 20 grades for her class. Of the 30 grades from another class, 10 were higher than Sarah's, and the rest were lower. If no other grade was the same as Sarah's grade, then Sarah's grade was what percentile of the grades of the two classes of two classes combined?

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #59411