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# A student is to answer 7out of 10 questions in an

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Joined: 10 Oct 2010
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A student is to answer 7out of 10 questions in an [#permalink]  14 Oct 2010, 07:43
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A student is to answer 7out of 10 questions in an examination .how many choices has she.how many if she must answer at least 3 of the first 5 questions
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Re: question [#permalink]  14 Oct 2010, 07:56
Expert's post
abeer16 wrote:
a student is to answer 7 out of 10 questions in an examination .how many choices has she.how many if she must answer at least 3 of the first 5 questions

Make sure you type the question in exactly as it was stated from the source.
Provide answer choices for PS questions.

As for your question, I guess question means that student must answer exactly 7 questions.

A student is to answer 7 out of 10 questions in an examination.
1. How many choices has she? Choosing different 7 questions to answer out of 10 - $$C^7_{10}=\frac{10!}{7!3!}=120$$;

2. How many if she must answer at least 3 of the first 5 questions? At least 3 out of firts 5 means 3, 4, or 5 out of first 5 questions (so 4, 3, and 2 question out of next 5): $$C^3_5*C^4_5+C^4_5*C^3_5+C^5_5*C^2_5=50+50+10=110$$.

Hope it's clear.
_________________
Re: question   [#permalink] 14 Oct 2010, 07:56
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# A student is to answer 7out of 10 questions in an

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