It depeds on which game you play. Card counting can certainly help but casinos don't like it. As far as roulette is concerned, betting on a color or on odds/evens gives you better odds than winning than if you were to bet on a single number.
yes there are many games which require some math for you to win the game but not all the time sometimes it may depend all on the luck for example the spin do not give any idea that at which point will it stop.