If we are to expand the exploration of our solar system, our next manned flight should be to Phobos, one of Mars's mo...

ritagentile August 10, 2020

Confused by answer choices B and E

I chose B for this question because it seemed like it gives a possible explanation for why the spaceship would need less fuel. I remember form the Paradox lecture that we need to find an answer choice that could be a possible explanation for the discrepancy, even if that answer choice is not necessarily true or "the case". So I'm confused why this would not work as the answer. What more information would it need to be the correct answer?

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shunhe August 11, 2020

Hi @ritagentile,

Thanks for the question! So remember what we’re told in the stimulus: we should go to Phobos and not Mars. Why? Because the flight times are the same, but the Phobos expedition would need less fuel and be less costly.

Now answer choice (B) tells us that smaller spaceships require less fuel than larger spaceships. OK, does this help resolve our paradox? Well, to answer that, we have to know about the relative sizes of the spaceships going to Mars and Phobos. Does the stimulus say anything about that? No, and we can’t just assume that the one going to Phobos is smaller. So (B) doesn’t actually help resolve the paradox! To answer the question on what more information we’d need for (B) to be the correct answer, we’d need to be told somewhere (either in the answer choice or the stimulus) that the spaceship going to Phobos is actually smaller than the one going to Mars. Then it would potentially resolve the paradox. But without knowing that, it does nothing, and we can’t just assume it for no reason. The only information we’re allowed to add to the stimulus is what’s given in the answer choice.

Hope this helps! Feel free to ask any other questions that you might have.