I got asked about this, but it looks like some responses have come in since then. However, I disagree with what Dimitri said a bit, so I want to correct.
1.There are times, as now, that learning grammar becomes important.
2. I will host the party if the guest list is less than fifty people.
The problem with this first one is that it isn't really a like/as issue at all. The first question should have "such as" now, not "as" now. "As" can ONLY be used in front of a clause if you're doing a comparison. This sentence doesn't feature it in a clause (it only has the word "now") in it. "Such as" would set up examples of times, of which "now" could be one. To repeat: I disagree with Dimitry. That is incorrectly written.
As for the second one, it's complicated. Technically, a guest list can't "be" fifty people. It could be "limited to fewer than fifty people", or "The guest list will feature fewer than fifty people." But to just use the straight verb makes no sense (either way, it would never be LESS with countable people.
ALSO: a correction of Dimitry. He wrote this sentence was correct: She played well this season, as in the season last year. "The season last year" has no verb, so it is not a clause. You'd have to say "like in the season last year".
Tommy Wallach | Manhattan GMAT Instructor | San Francisco
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