erikstrand

I think you're looking for a factorial number system [1] and/or Lehmer code [2].

[1] https://en.wikipedia.org/wiki/Factorial_number_system [2] https://en.wikipedia.org/wiki/Lehmer_code

For context, in the US there are 15.3 million students enrolled in high school, 3.7 million of which are expected to graduate this year (i.e. a little under a quarter, as one would expect) [1]. So the 2.2 million graduate test takers mentioned in the WSJ article represent about 60% of the pool of fresh high school graduates.

Also given the surrounding numbers sum to 100%, I'm guessing the author meant to say 56% percent of SAT test takers have parents with a college degree, rather than "56% of students whose parents have a degree took the test". Probably just a careless mistake, but I still find it ironic (or perhaps indicative) that no editors caught it even though it appears a few sentences after "students struggled most in math".

[1] https://nces.ed.gov/fastfacts/display.asp?id=372#PK12_enroll...