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Math Help - Statistics - Proportion

  1. #1
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    Statistics - Proportion

    A student is to answer 7 out of 10 questions in an examination. How many choices are there? How many choices are there if at least 3 of the first 5 questions have to be answered? [Hint: split exam into the first 5 and last 5 questions].
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  2. #2
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    "At least 3 of the first 5".

    We can choose 3 from the first 5, 4 from the first 5, or 5 from the first 5.

    That leaves 4 from the remaining 5, 3, and 2 respectively.

    \binom 5 3\cdot\binom 5 4+\binom 5 4\cdot\binom 5 3+\binom 5 5\cdot\binom 5 2
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  3. #3
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    Ouch, i got 105 outcomes? =/ This is my first time doing stats at uni lol, At alevel I only done mechanics modules so I'm struggling big style :S
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