I posted a solution here:

https://www.beatthegmat.com/og-12-q-ds-t77873.html

rommysingh wrote:The annual rent collected by a corporation from a certain building was x percent more in 1998 than in 1997 and y percent less in 1999 than in 1998. Was the annual rent collected by the corporation from the building more in 1999 than in 1997?

(1) x > y
(2) xy/100 < x-y

The first thing to getting the right answer to this one is avoiding getting tricked by Statement 1, which incorporates a trick pretty commonly used in GMAT questions.

Statement 1 seems to be saying that the increase from 1997 to 1998 is greater than the decrease from 1998 to 1999, but that is not necessarily the case.

For instance, if the rent collected were 100 in 1997 and went up x = 25% to 125 in 1998, if y were only 20%, the rent collected would go from 125 in 1998 to 125 - 25 = 100 in 1999. So y is significantly less than x in this case, but the absolute change in rent collected is the same, and the rent collected in 1997 is the same as that collected in 1999 even though x is greater than y.

One could create other scenarios in which x > y, and in some the rent collected in 1999 would be higher than that in 1997, and in others it would be lower.

So while Statement 1 may look sufficient at first glance, actually it is insufficient.

Learning to not get tricked by differences in percentage changes that are different from differences in absolute changes can be key to avoiding choosing a wrong DS answer.