Geometric mean annual increase from $651M (1998) to $2.4B (2001)

[bubble1421]

I don't know why I can't figure this one out tonight. I just can't think straight and I am hoping someone can help ASAP.

Here is the question:
In 1998 revenue from gambling was $651 million. In 2001 the revenue increased to $2.4 billion. What is the geometric mean annual increase for the period?

 

[mathman]

Since the difference in the number of years is 3, you have to take the cube root of the ratio to get your result.