Rodents are small, gnawing mammals characterized by their chisel-like incisor teeth.
Information
Since we read Must Be True looking primarily for Conditional, Math-y, or Causal ideas, we would be most attracted to the two Most claims.
Most NA mammal species are not rodent species. but Most individual mammals in NA are rodents.
Evaluate
There are a couple famous inferences we can make with two Most statements, but this example is neither of them. (Here they are, for reference, though)
Most A's are B Most A's are B Most A's are C Most B's are ~A infer: Some B's are C more B's than A's
However, we can tell that we're supposed to do something mathematical by reconciling those two most claims.
It's sort of a paradox -- GIVEN THAT most species are not rodent species, HOW CAN IT BE most individuals are rodents?
Let's pretend we're at a restaurant that forbids co-ed seating. It's either all men eating at a table together or all women eating at a table together.
What could we infer from this pair of statements? Most of the tables are not female-tables. but Most of the individual people eating at the restaurant are females.
If women are responsible for a minority of tables at the restaurant but a majority of people at the restaurant, then there must be more women sitting per table.
10 tables with 5 women each = 50 women 12 tables with 4 men each = 48 men
Out of the 22 tables, most of them aren't female tables (10 of 22), but out of the 98 individuals, most of them are females (50 of 98).
Goal
Similarly, if most species aren't rodents, but most individuals are rodents, then there must be more rodents per rodent species than there are non-rodents per non-rodent species.
(Just like there were more women per female-table than there were men per male-table ... also, my apologies to womankind for making them the rodents in this math metaphor)