Type in the Input. The Function Machine applies the function and produces the Output. If you choose [Random], you will have to use some brainpower to figure out the hidden function.
http://www.amblesideprimary.com/ambleweb/mentalmaths/functionmachines.ht...

Linear Function Machine
With this function machine, you have to enter the correct linear function, using algebra.
http://www.shodor.org/interactivate/activities/LinearFunctMachine/