Thanks for the question! So let’s take a look at this stimulus. We know that 30% of houses have inadequate site drainage. We also know that 30% have unsafe structural defects. The argument then concludes that at least 60% of the houses have some problem that threatens their integrity.
Seems pretty simple, right? 30+30=60, so this has to be right. But we know there’s a flaw in the argument that we’re looking for, and during our prephrase, we should realize that there’s a possibility that the argument isn’t accounting for. These two concepts aren’t mutually exclusive. A house could have inadequate site drainage AND unsafe structural defects. And if there is overlap, then the conclusion doesn’t necessarily follow. For example, what if the 30% of houses in the town with inadequate site drainage are the same 30% of houses that are made unsafe? Then, only 30% of the town houses would have some problem threatening their integrity. This is what (E) tells us: some of the houses that have unsafe structural defects could also have inadequate site drainage; there could be some overlap between these two groups.
(D), on the other hand, doesn’t point out this problem. It tells us that many houses in the town could have neither inadequate site drainage nor unsafe structural defects. But remember that “many” on the LSAT really could just be a few. In fact, it’s possible for at least 60% of the town houses to have some kind of problem, and “many” houses to have none—the other 40%! So (D) doesn’t really explain the problem with the argument, and we can eliminate it.
Hope this helps! Feel free to ask any other questions that you might have.
