Every student in a class swims, dances, or does both. Three fifths of the class swim and three fifths dance. Five students both swim and dance. How many students are in the class?
Pure mathematics is the world's best game. It is more absorbing than chess, more of a gamble than poker, and lasts longer than Monopoly. It's free. It can be played anywhere - Archimedes did it in a bathtub.
Richard J. Trudeau, Dots and Lines
Learn mathematics better and solve your own problems.