I am a mathematics graduate student and am currently writing a cover letter. The main reason I decided to study mathematics (bachelor back then), was because I found mathematics really difficult. If I was going to spend three years in college, I wanted to challenge and improve myself.
Is there a word or phrase to describe something that was once difficult but now easy? The best thing I could come up with was "I have grown accustomed to" but this does not represent the effort I put into mastering math nor does it describe I now actually do find it easy.