Math.Pow can't handle fractions ?

Question

Hello,

I saw this problem today.
I used to calculate this: varX = Math.Pow(varx, 1/3);
Everytime I get only an integer that is completly wrong!
But if I use this: varX = Math.Pow(varx, 0.333333);
Then the result is allright...
What is wrong with this function?
I can't express 1/3 as a double number cause it's endless.

Please help me...