Answering the easy questions first is a worthwhile test-taking?

I definitely think so because doing to harder ones waste time. For instance, yesterday I was doing math questions and the the last one I did was extremely hard and took like 15 minutes while the others took 7-8.

I believe so! You can knock them out pretty quickly, then focus the majority of your remaining time on the harder questions. By doing this you don't have to worry about doing the easy problems later. :)