OG11-SC77: less as a noun?

cavinmontrea

Q: Even though the direct costs of malpractice disputes ________  than 1 percent of the $541 billion the nation spent on health care last year, doctors say fear of lawsuits plays a major role in health-care inflation.

(A) amounts to a sum lower
(B) amounts to less
(C) amounted to less
(D) amounted to lower

OG gave the correct answer C and explained that a noun less is required as the object of the preposition to. But how to understand less (noun)+than ...?

Thanks

joe11

direct cost amounted to less than 1%

amounted v. + to. prep.

  Since "to" is a prep. here, Noun is expected after a prep. -> "less" is a noun in the sentence.

cavinmontrea

Thanks.

Then is than a preposition?