Question

100 + 95 + 90 + 85 summation notation series solution

Answer 1

Since we are decreasing by 5 each time, we can build up a series formula first.
$S_n = \frac{n}{2}(2a + (n - 1)d)$
$S_n = \frac{n}{2}(200 - 5(n - 1))$

Now, adding summation notation, we produce:

$\sum_{k = 1}^{n}[\frac{k}{2}(200 - 5(k - 1))]$