Arithmetical MEAN

Arithmetical MEAN, is half the sum of the extremes. So 4 is an arithmetical mean between 2 and 6, or between 3 and 5, or between 1 and 7; also an arithmetical mean between $a$ and $b$ is $\backslash frac\{a+b\}\{2\}$, or $\backslash frac\{1\}\{2\}a\; +\; \backslash frac\{1\}\{2\}b$.