Scripting: Random Number
The command processor (CMD.EXE) will dynamically resolve the environment variable %RANDOM% to a random integer between 0 and 32767.
To return a number to the variable R between 0 and an upper limit n inclusive, use the modulo syntax (%% in a script, % from the command line):
set /A R=%Random% %% n+1
To return a number between m and n, use:
set /A R=%Random% %% (n-m+1) + m
For example, to return a random number between 10 and 20 inclusive:
set /A R=%Random% %% 11 + 10