100 students appeared for two different examinations. 60 passed the first , 50 the second and 30 both examinations. Find the probability that a student selected at random failed in both examinations?
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
As for everything else, so for a mathematical theory: beauty can be perceived but not explained.