Effect:
The cube root demonstration begins by asking members of
the audience to select any number from 1 through 100, cube it, then
call out the result. The performer instantly gives the cube root
of each number called.
Method:
Described in 'Mathematics, Magic and Mytery'
(Martin Gardner 1956).
Training:
I'm going to pick a number between 1 and 100 and then I cube it.