Prime just returns the entered function

[RickyFlips]

When I enter certain functions involving unspecified variables, my expectation is that the Prime will return a simplified version of the function or an interim result, but instead my Prime returns the function as-entered (CAS) or 0 (Home). Examples:

   

What I'd expect returned is the function simplified: -2.5*e^(-50*x) + 6.25*e^(-10*x)

   

What I'd expect here is an interim result, like: ln[b] - ln[a]

I've tried the "simplify" soft button, as well as the different "Simplify" settings, and I've searched both Google and here, but haven't found an answer yet. This would be immensely helpful, since simplifying by hand is commonly where I make a mistake. So, is there a way to get my Prime to do this?

Thanks!