Mental calculation
Mental calculation or mental maths is an old mathematical tool. It is doing maths without using any objects or writing anything down. Mental calculation uses only the human brain. People who use mental maths use shortcuts to make the calculation easier. People who use mental calculation do not use a computer or a calculator.
Calculation methods
There are some methods to do mental maths. One way to do multiplications is the Russian peasant multiplication. An other way to do multiplications with two numbers is to use binomial formulas.
[math]\displaystyle{ (x+y) \cdot (x-y)= x^2 - y^2 }[/math]