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I got this math question wrong, but I'm not exactly sure why.

Here's the question:

If all alligators are ferocious creatures and some creepy crawlers are alligators, which statement(s) must be true? 

  I. All alligators are creepy crawlers.
 II. Some ferocious creatures are creepy crawlers.
III. Some alligators are not creepy crawlers.

(A) I only (B) II only (C) III only (D) II and III Only (E) None of these must be true

The answer was (B) II only, but I got (A) I only. My reasoning was that since some creepy crawlers are alligators, then in the group of creatures that are creepy crawlers, alligators are amongst them, therefore assuming that all alligators are creepy crawlers. I know that there is some flaw in my reasoning so can someone point it out for me?

Andrew Hu
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    For statement (A) to be true, you'd need all aligators to be creepy crawlers. You only know that some creepy crawlers are alligators. Not only does this leave room for non-alligator creepy crawlers, but it also leaves room for some alligators to not be creepy crawlers. – Raskolnikov Aug 26 '13 at 06:24
  • @Raskolnikov You should post that as an answer so this doesn't show up on the unanswered queue. Thanks. – Potato Aug 26 '13 at 06:35

1 Answers1

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For statement (A) to be true, you'd need all aligators to be creepy crawlers. You only know that some creepy crawlers are alligators. Not only does this leave room for non-alligator creepy crawlers, but it also leaves room for some alligators to not be creepy crawlers.

Here's an example that's easy to grasp: some real numbers smaller than 1 are bigger than -1. Can you therefore conclude that all numbers bigger than -1 are smaller than 1?

Raskolnikov
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