If that's your goal, the languages need to be from different paradigms (maybe C + Assembly, Ruby/Python, and Haskell/Clojure, and then maybe Prolog and Factor).

If that's your goal, the languages need to be from different paradigms (maybe C + Assembly, Ruby/Python, and Haskell/Clojure, and then maybe Prolog and Factor). If your goal is just to get someone to minimum competence so they can build something, it's better to stick with one language (or, at worst, just a web stack), at the very least so they don't get bogged down installing a bunch of tools for relatively little benefit. PHP and Ruby are both Algol derivatives, so having a person solve Project Euler problems in both and compare them won't likely reveal much more than trivial differences. Also, unless they have a decent math background, 100 Project Euler problems is just going to frustrate and scare off people - some of those problems are pretty much intractable without Dynamic Programming; anyone who hasn't taken an algorithms course would probably take a long time to figure that out.