Tom  Jackson
Tom Jackson answered

From the Internet---

The Fundamental Principle of Counting:

If something can be chosen, or can happen, or be done, in m different ways, and, after that has happened, something else can be chosen in n different ways, then the number of ways of choosing both of them is 

m · n.


Danae Hitch
Danae Hitch answered

The abacus, also called a counting frame, is a calculating tool that was in use in Europe, China and Russia, centuries before the adoption of the written Hindu–Arabic numeral system.

The exact origin of the abacus is still unknown. Today, abaci are often constructed as a bamboo frame with beads sliding on wires, but originally … Read more