1993 AHSME Problems/Problem 21

Problem

Let $a_1,a_2,\cdots,a_k$ be a finite arithmetic sequence with $a_4 +a_7+a_{10} = 17$ and $a_4+a_5+\cdots+a_{13} +a_{14} = 77$ .

If $a_k = 13$ , then $k =$

$\text{(A) } 16\quad \text{(B) } 18\quad \text{(C) } 20\quad \text{(D) } 22\quad \text{(E) } 24$

$\fbox{B}$ why?

1993 AHSME (Problems • Answer Key • Resources)
Preceded by Problem 20	Followed by Problem 22
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