CEMC Euclid, 1998

Algebra Difficulty 3.0 AMC 10/12 Prove it Canada

The $n$ th term of an arithmetic sequence is given by $t_n=555-7n$ . If $S_n=t_1+t_2+\cdots+t_n$ , determine the smallest value of $n$ for which $S_n<0$ .

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