Overall gap of 46
Here's a stupid qeustion that I am being confused about what exactly the"overall gap of 46 percentaged points" refers to in the last setence of the following paragraphs ：
Consider the teenagers who scored among the top 25 percent of students on the math test. In this group, the students from the top socioeconomic quartile had very high bachelor’s degree completion rates: 74 percent of the most advantaged students with top math scores earned a four-year college degree by the time they were in their late 20s.
But only 41 percent of the poorest students with the top math scores did so. That’s a completion gap of 33 percentage points, not much smaller than the overall gap of 46 percentage points.
Thanks a lot in advance !!!