Question 354181
A jar contains 9 blue marbles and 13 green marbles. Two marbles are picked in
sequence from the jar. Find the probibility that the second marble is green
given that the first marble is blue(assume that the first marble is not
replaced).
<pre>
There are 9+13 or 22 marbles.  So 9 twenty-seconds, ({{{9/22}}}nds) of the time
we will select a blue marble first.

If we then don't replace it, then after picking that blue marble, there will
remain only 8 blue marbles and 13 green marbles, or 8+13 or 20 marbles.  

Then 13 twenty-firsts ({{{13/21}}}sts) of those times when we pick a blue
marble first, we will pick a green marble second.

So the answer is gotten by taking {{{13/21}}}sts of those {{{9/22}}}nds of the
times when we pick a blue marble first.  So the answer is

{{{(13/21)*(9/22)}}}

{{{(13*9)/(21*22)}}}

   {{{3}}}
{{{13/cross(21)*cross(9)/22)}}}
{{{7}}}

{{{(13*3)/(7*22)}}}

{{{39/154}}}   

Edwin</pre>