The above problem asks for the number of hours needed for a post that triples its number of shares every hour to reach 1000 shares given that it starts with 5 shares. I guess this is more of a reading comprehension question, but shouldn’t the answer be 4 hours? At 4 hours it has 405 shares, and at 5 hours that grows to 1215. So the required time is somewhere between 4 and 5. In other words, it only takes 4 hours (and some number of minutes) to get there, not 5 hours. I think I’d get tripped up by the wording if this was the actual GRE.
The literal wording is “If the post started with 5 shares at 1:00 PM, how many hours would it take it to have over 1000 shares?”. You’re right that we’re not there at exactly four hours - but it doesn’t take 5 either, it will be something like 4:45 or whatever. Since it’s asking for how many hours it takes, I don’t see why 5 is necessarily a better answer than 4 - it doesn’t take five whole hours. If the rate of growth were more abrupt, we might even be able to manufacture a situation where we reach 1000 shares in 4 hours and 1 minute!
I would agree with LemonIceTea9. The question is asking for the number of hours for the number of shares to be over 1,000. After four hours, would that be the case? No.