There was a typo...

I'm confused. The answer was n(n+1), but the options were:
i.) 1/(n(n2))
ii.)1/(2n2)
iii.)1/(2n)
iv.)1/(n(n1))I guessed iv.) even though none of them seemed to work and the answer said: "All the denominators have the form n(n+1)." I think there was a typo in which there was a minus sign where there should have been a plus sign. Can you fix that?