By learning this simple system you will be able to instantly calculate the cube root of the spectator's number.
Ask the spectator to choose any whole number less than 100 and, using a calculator, to find its cube by multiplying the number by itself, then multiplying the answer by the original number.
Alternatively, if the spectator knows how to use scientific calculator, they can enter the original number, then press the "x^y" key followed by 3 and =.
The spectator then calls out the answer, and you instantly reveal the original number (i.e., the cube root).
Note that this method will not work with cubes of numbers greater than 99. Also the method only works when the cube root is a natural number (integer).