- #1

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## Homework Statement

The problem is as shown in the attatchment.

## Homework Equations

The relevant equations are also given in the attatchment.

## The Attempt at a Solution

My problem is how to adapt the given formula in order to find the sum of the function k(40-r)

Do i use the formula for 1 to 40, then 1 to 20 and subtract?

Even just a hint in the right direction would be useful. This sorta stuff has never been my strong point.