Anna B.

asked • 06/30/17

How many questions do I need to study?

my professor gave us 14 questions to study for the exam. he will list 7 of them on the exam. out of these 7, we only have to answer 4. how many out of the 14 questions do i need to study to be sure i can answer 4 of the 7 questions on the exam

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David C. answered • 06/30/17

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Anna B.

I can choose which 4 questions (out of the 7) I want to answer. Wouldn't that mean that I only have to study 11 questions to be sure I can answer 4?
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06/30/17

Arturo O.

OK, I can see that.  If you know 11, you do not know 3.  Then the worst case scenario is that the 3 you do not know will be on the test, but that must leave 4 that you do know.
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06/30/17

David C.

Thanks Arturo! 
Disregard my 14 answer. 
 
Arturo is correct.
 
I misread the question....probably up to early...
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06/30/17

David W.

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Many problems and situations are best analyzed by starting with, "What is it not?"
 
Here, of the 7 test questions, we may miss, at most, 3.  So, if you don't study (that assumes that "study" means getting the correct answer and "not study" means getting the wrong answer) at most 3, you still pass.
 
The test questions come from a pool of 14, so only 3 may be incorrect (not studied).  That leaves 11 that you must answer correctly (or "study").
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06/30/17

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