How do you find the sum of the arithmetic sequence having the data given $a_1= 5$ , $a_n = 3$ , n = 20?

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Answer 1 · 2016-02-06T15:07:56

The information give gives you the first term, the last term and the number of terms. This means we can use the formula $S_n = (n/2)(a + t_n)$ .

$S_20 = (20/2)(5 + 3)$

$S_20 = 10(8)$

$S_20 = 80$

Your sum is 80.

How do you find the sum of the arithmetic sequence having the data given a_1= 5a_1= 5, a_n = 3a_n = 3, n = 20?