document.write( "Question 169882: A box contains 74 brass washer, 86 steel washers and 40 aluminium washers. Three washers are drawn at random from the box without replacement.\r
\n" ); document.write( "\n" ); document.write( "a) Determine the probability that all three are steel washers.\r
\n" ); document.write( "\n" ); document.write( "b) Determine the probability that there are no aluminium washers drawn, when three washers are drawn at random from the box without replacement.\r
\n" ); document.write( "\n" ); document.write( "c) Find the probability that there are two brass washers and either a steel or an aluminium washer when three are drawn at random, without replacement. \n" ); document.write( "

Algebra.Com's Answer #125315 by Edwin McCravy(20060) $\"\"$ $\"About$

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Warning: Stanbon's
\n" ); document.write( "(b) and (c) are incorrect.
\n" ); document.write( "Edwin's solution:\r
\n" ); document.write( "\n" ); document.write( "A box contains 74 brass washer, 86 steel washers and 40 aluminium washers. Three washers are drawn at random from the box without replacement.
\n" ); document.write( "a) Determine the probability that all three are steel washers.
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document.write( "There are 86 steel washers.\r\n" );
document.write( "There are  or  washers.  So the\r\n" );
document.write( "desired probability is\r\n" );
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document.write( " 86 choose 3\r\n" );
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document.write( "200 choose 3\r\n" );
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\n" ); document.write( "b) Determine the probability that there are no aluminium washers drawn, when three washers are drawn at random from the box without replacement.
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document.write( "There are 74+86 or 160 non-aluminum washers.  (This can also be calculated\r\n" );
document.write( "by subtracting the 40 aluminum washers from the total 200, i.e., 200-40=160.)\r\n" );
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document.write( " 160 choose 3\r\n" );
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document.write( " 200 choose 3\r\n" );
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\n" ); document.write( "c) Find the probability that there are two brass washers and either a steel or
\n" ); document.write( "an aluminium washer when three are drawn at random, without replacement.
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document.write( "There are 74 brass washers.\r\n" );
document.write( "There are 86+40 or 126 washers that are either steel or aluminum.\r\n" );
document.write( "So the desired probability is\r\n" );
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document.write( " (74 choose 2) + (126 choose 1)\r\n" );
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document.write( "       200 choose 3\r\n" );
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document.write( "Edwin

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