You are correct and I edited it to include that if we had information about median test scores, we would know more. But I think it is reasonable to guess that if the 25-75% is 720-790, that the median SAT Math score at Dartmouth likely falls below 780. The overall scores on the Verbal are higher at Dartmouth, but given that the top 25% at Michigan is 730 or higher, and the bottom 25% at Dartmouth is 700 or lower, that number would obviously be higher than the “bottom 25%”. And given that 25% of the Dartmouth students have a composite score of 31 or below on the ACT and the top 25% at Michigan is 34 and higher, the “bottom 25%” estimate is wrong.
But again, I think that your perception supports my point about why rich people prefer elite schools for their kids.