In 1990, an article in the New York Times informed that researchers have found that "it takes just seven ordinary, imperfect shuffles to mix a deck of cards thoroughly".

Whenever we are shuffling cards, preparing a dough or analyzing industrial processes, the mixing problem appears naturally: how much mixing do we need to do until a reasonably uniform mix has been achieved?

In this talk we will try to explain how can we answer this question using mathematics, and in particular probability theory.