How many ways can two marbles be chosen from a set of five marbles?
5
10
15
20

Bolivia is a nation located in the continent of South America, bordering Argentina, Brazil, Chile, Paraguay and Peru. It is located in the center of the continent, which gives it a remarkable range of ecosystems: to the west is the Andes Mountains and the puna, an area of high altitude and great aridity; while to the east there are flat areas, suitable for agriculture and livestock; in turn, to the north is the beginning of the Amazon jungle. Its capital is Sucre, and its most important city is La Paz.

It is a country that does not have direct access to the sea, which largely explains the certain economic and social backwardness that it has as a nation: its almost 13 million inhabitants are among the poorest in South America.