A randomized strategy or a convex combination may be represented by a
probability vector p = (p1,..., p(m)). p is called sparse if it has fe
w positive entries. This paper presents an approximation lemma and app
lies it to matrix games, linear programming, computer chess, and unifo
rm sampling spaces. In all cases arbitrary probability vectors can be
replaced by sparse ones with only logarithmically many positive entrie
s) without losing too much performance.