The sequence s_1, s_2, s_3, ... , s_n, ... is such that s_n= \frac{1}{n} -\frac{1}{n+1} for all integers n\geq 1. If k is a positive integer, is the sum of the first k terms of the sequence greater than \frac{9}{10}?
(1) k>10
(2) k < 19
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