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Math Help - 2 probability problems

  1. #1
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    2 probability problems

    a) 16 men were at work demolishing an old factory when part of it collapsed, injuring 3 of them. Three of the men were apprenticies

    Calculate the probability that all 3 men were apprenticies??

    b) Out of 40 paving slabs, 12 have internal cracks.

    Determine the probability that, in choosing 5 slabs at random, a cracked slab is not selectedů.

    answers for a is 1/560
    b = 105/703

    but how??
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  2. #2
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    \left( {\begin{array}{*{20}c}<br />
   {16}  \\<br />
   3  \\<br /> <br />
 \end{array} } \right) = \frac{{16 \cdot 15 \cdot 14}}<br />
{{3 \cdot 2 \cdot 1}} = 560

    There 560 ways to choose 3 men from 16.
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  3. #3
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    :)

    Quote Originally Posted by Plato View Post
    \left( {\begin{array}{*{20}c}<br />
{16} \\<br />
3 \\<br /> <br />
\end{array} } \right) = \frac{{16 \cdot 15 \cdot 14}}<br />
{{3 \cdot 2 \cdot 1}} = 560

    There 560 ways to choose 3 men from 16.
    ah I see its a dependant event

    hmm going to try second one again
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