mberkowitz wrote:does this mean, if 50 is in S, than 51 is in S. and if 51 is in S, then 52 is in S. And so on until 100 and beyond?

If so, thats a crime to all well-written gmat problems.

Yes, that's the intended meaning, which is why A is sufficient. B is not sufficient, because the smallest thing in the sequence might be 150 or 145 or something else which is larger than 100.

I've seen this question before on this forum, though I don't know the source. The wording above is indeed horrible, but I'm pretty sure the wording was much better the last time I saw it, so I wonder if the wording above is truly the original wording. For one thing, the question should not refer to a 'series'; it's describing either a set or a sequence. It's also a run-on sentence, so could serve double duty as an exercise in Sentence Correction.