document.write( "Question 700038: There are three urns:first urn contains 1 white,2red,3green balls,second urn contains 2 white,1red,1green balls and third urn contains 4 white,5red,3green balls.
\n" ); document.write( "Two balls are drawn from an urn chosen at random.These are found to be one white and one green.Probability that balls are drawn from third urn is:
\n" ); document.write( "(A)15/59, (B)14/59, (C)13/59, (D)12/59\r
\n" ); document.write( "\n" ); document.write( "Please explain the procedure also!In book only the correct answer is given 15/59....but i dont get how to slove it,so plz explain the procedure,plz.
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Algebra.Com's Answer #431811 by KMST(5328)\"\" \"About 
You can put this solution on YOUR website!
DISCLAIMER:
\n" ); document.write( "I do not memorize procedures, and I do not follow procedures unless someone makes me.
\n" ); document.write( "What follows is my just my understanding of the problem.
\n" ); document.write( "Your teacher may have a procedure to reach the solution more efficiently.
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\n" ); document.write( "If an urn chosen at random, the third urn will be chosen \"1%2F3\" of the times.
\n" ); document.write( "(In fact, each of the three urns will be chosen \"1%2F3\" of the times).
\n" ); document.write( "
\n" ); document.write( "If the first urn is chosen (with 6 balls, including 1 white and 3 green),
\n" ); document.write( "the probability of drawing the white ball first is \"1%2F6\".
\n" ); document.write( "After that, the probability of drawing one of the 3 green balls from the 5 balls left in the urn is \"3%2F5\".
\n" ); document.write( "So, the probability of drawing a white ball followed by a green ball from the first urn is \"%281%2F6%29%283%2F5%29=1%2F10\".
\n" ); document.write( "Similarly, the probability of drawing a green ball followed by a white ball from the first urn is \"%283%2F6%29%281%2F5%29=1%2F10\".
\n" ); document.write( "The probability of drawing a white ball and a green ball (in any order) from the first urn is \"1%2F10%2B1%2F10=1%2F5\".
\n" ); document.write( "
\n" ); document.write( "If the second urn is chosen (with 4 balls, including 2 white and 1 green),
\n" ); document.write( "the probability of drawing a white ball and a green ball (in any order) is
\n" ); document.write( "\"%282%2F4%29%281%2F3%29%2B%281%2F4%29%282%2F3%29=1%2F6%2B1%2F6=2%2F6=1%2F3\"
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\n" ); document.write( "If the third urn is chosen (with 12 balls, including 4 white and 3 green),
\n" ); document.write( "the probability of drawing a white ball and a green ball (in any order) is
\n" ); document.write( "\"%284%2F12%29%283%2F11%29%2B%283%2F12%29%284%2F11%29=1%2F11%2B1%2F11=2%2F11\"
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\n" ); document.write( "If the drawing of two balls was done \"3%2A%283%2A5%2A11%29=3%2A165\",
\n" ); document.write( "you would expect the first urn to be chosen 165 times,
\n" ); document.write( "drawing one a white ball and a green ball (in any order) from the first urn
\n" ); document.write( "\"165%281%2F5%29=3%2A5%2A11%282%2F5%29=3%2A11=highlight%2833%29\" times.
\n" ); document.write( "The second urn would be also chosen 165 times,
\n" ); document.write( "drawing one a white ball and a green ball (in any order) from the second urn
\n" ); document.write( "\"165%281%2F3%29=3%2A5%2A11%281%2F3%29=5%2A11=highlight%2855%29\" times.
\n" ); document.write( "The third urn would be also chosen 165 times,
\n" ); document.write( "drawing one a white ball and a green ball (in any order) from the third urn
\n" ); document.write( "\"165%282%2F11%29=3%2A5%2A11%282%2F11%29=3%2A5%2A2=highlight%2830%29\" times.
\n" ); document.write( "
\n" ); document.write( "In all, a white ball and a green ball (in any order) would be drawn (from an urn chosen at random)
\n" ); document.write( "\"33%2B55%2B30=118\" times.
\n" ); document.write( "Of those 118 times, 30 times it would be from the third urn,
\n" ); document.write( "so if a white ball and a green ball (in any order) had been drawn
\n" ); document.write( "\"30%2F118=highlight%2815%2F59%29\" of the times it would have been using the third urn.
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