Is this a joke?!

I was flipping through an old math trick book that I have. It tries to teach you sort of "math shortcuts". I come upon the cube root section. As I was reading it over, My brain seemed so come to a sudden halt as i realized how stupid it really was. It goes like this:
Know the cubes of all numbers 1-9:
1-1
2-8
3-27
4-64
5-125
6-216
7-343
8-512
9-729
Choose a number, 1-999999. (we shall choose 324521).
Split the number into two groups of three, starting from the right:
324 521
Now, take the last number in the second group (1). Find the cube of a number 1-9 that ends in this number(1^3 ends in 1)
The 1 is the second number of the cube.

Now, take the first group of numbers, and find out between which two cubes of numbers 1-9 it lies, and choose the smallest of the two(324 is between 216 and 343, so we choose 6). This is the first number of the cube. Going by this method, 61 is the cube root of 324521, while 61^3 is ~100000 less then 324521...

I wanted to cry.

I just thought I would share this sad sad tale with you guys =).

Z.

As a trick it seems to work for whole number roots, ask someone to pick any number and tell you the cube. In a very short time you could find their original number - a lot faster than they worked out the cube with pencil and paper.

That is true. It works pretty well for perfect, or almost perfect cubes, but it is very dependant on the last number of the cube.

Z.
[edit]
Although the book never actually says that -.-