What is the sum of all even numbers from 1 to 160?

If the question excludes the endpoint 160 then: I guess that you could reason as follows:

2 + 158 = 160

4 + 156 = 160

...

78 + 82 = 160

There are 39 pairs that add up to 160 plus one 80 that is not paired.

(39 * 160) + 80 = 6320

If the question is meant to include the endpoint 160 ,then (40 * 160) + 80 = 6480