You have to be more specific about percentage changes: is it INCREASING from $399 to $649, or is it DECREASING from $649 to $399??.
If It is INCREASING, then: 649 / 399 =1.6266 -1 x 100 =62.66% increase.
If it is DECREASING, then: 1 - (399/649) x 100 =38.52% decrease.
