Question 89
What is the sum of the first 13 terms of an arithmetic progression if the first term is -10 and last term is 26?
Solution
$$S_{n}=\frac{n}{2}[a+l]$$
$$S_{13}=\frac{13}{2}[-10+26]$$
$$S_{13}=\frac{13}{2}[16]=104$$
So the answer is option A.
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