On the 25 k/d spread. how does the math work on this bounty?

if you go +5 one match then -2 the next match do you end up at +5 towards the bounty or do you end up at +3? Trying to help a friend here and I've never done this bounty

You'd end up with +3, however assists count towards the total also, so you could not get any kills at all and finish the bounty as long as you're getting more assists than deaths.