Depends how aggressive you want to be with it but I would spilt it up into 5 bits then pick 2 coins from the top 25, another 2 from the top 25-200, and then one coin outside that for a pure gamble. That way you diversify and at the same time are in some solid coins too.
Seriously speaking its just $50. Even if he invests it strategically he wont be able to make much return from it. The max he will be able to do is x4-5 which wont be much given the risk and how long he will have to wait for it. Also you are better off trying to trade that amount to try to at least double it before investing it for the long term.