Milo has a collection of dvds. out of 45 dvds, 40% are comedies and the remaining are action-adventures. how many action-adventure dvds does milo own?

Milo owns 27 action-adventure DVDs.

45 (total) x 0.4 (% of comedies) = 18 (# of comedy DVDs).
45 - 18 = 27 (# of action-adventure DVDs)

Or

100 (total %) - 40 (% of comedies) = 60 (% of action-adventures)
45 (total) x 0.6 (% of action-adventure DVDs) = 27 (# of action-adventure DVDs)