Among X Between

Well, the difference between among and between can be a complex question. To keep it simple, between is used for two items and among is used for three or more items.
For example:
The money was split between the two girls.
The money was split among all four girls.
It was hard to choose between two very highly rated schools.
It's difficult to choose among the five very highly rated schools.

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If you want a deeper explanation on this topic, check this out: http://grammar.quickanddirtytips.com/between-versus-among.aspx