Grinnell and Trinity are liberal arts colleges (LACs); neither one offers a business major.
Richmond sometimes is classified as a LAC (by USNWR, for example), but it does have a business school. It has undergraduate accounting and business administration majors. According to its CDS about 36% of its students major in “Business/marketing”. So if you think you might want to major in business, Richmond may be your best choice.
If you are serious about mathematics, especially pure math, Grinnell might be a better choice.
FWIW Grinnell seems to rank perennially among the top 10 (or so) colleges for per-capita rate of alumni-earned PhDs (across many fields, including math/sciences AFAIK).
That does not necessarily mean Grinnell’s math instruction is far better than Trinity’s or Richmond’s.
It does suggest to me that, for whatever reason, Grinnell may be attracting a higher percentage of students who (either when they enter, or by the time they graduate) are more motivated or better prepared to study certain fields (possibly including math) at the highest level. But try comparing the course offerings, requirements, and online faculty bios to see if Grinnell’s program seems to be stronger in areas that might interest you.
I wouldn’t say Trinity is “lowly ranked” (assuming you’re talking about the one in Hartford, Connecticut). All 3 of these schools have very high sticker prices and will enroll many students whose families are affluent enough to cover the full cost. Another concern about Trinity may be the location, which apparently is not too attractive (although the campus itself is beautiful). Can you visit?