Question

What is the sum of the finite arithmetic series?

(–5) + 0 + 5 + 10 + ... + 65

900
455
450
445

Answer 1

(–5) + 0 + 5 + 10 + ... + 65

5(-1 + 0 + 1 + 2 + ... + 13)

5(1 + 2 + 3 + ... + 13) - 5

\(\displaystyle\large \left(5\sum_{n=1}^{13}n\right) - 5\)

Answer 2

\[5 \sum _{n=1}^{13} n-5=450 \]

Answer 3

Is this clear, @vivianrush ?