document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=263800>Question 263800</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A box contains some green marbles and exactly four red marbles. The probability of selecting a red marble is x%. If the number of green marbles is doubled, the probability of selecting one of the four red marbles from the box is (x – 15)%. How many green marbles are in the box before the number of green marbles is doubled? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #194371 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=194371\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A box contains some green marbles and exactly four red marbles. The probability of selecting a red marble is x%. If the number of green marbles is doubled, the probability of selecting one of the four red marbles from the box is (x – 15)%. How many green marbles are in the box before the number of green marbles is doubled?<BR>\n" );
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document.write( "Original setup<BR>\n" );
document.write( "P(1 red) = 4/(g+4) = x/100<BR>\n" );
document.write( "Then g + 4 = 4/x/100<BR>\n" );
document.write( "g = (4/(x/100))-4<BR>\n" );
document.write( "g = (400/x) -4<BR>\n" );
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document.write( "New setup<BR>\n" );
document.write( "P(1 red) = 4/(2g+4) = (x-15)/100<BR>\n" );
document.write( "(2g+4) = 400/(x-15)<BR>\n" );
document.write( "g+2 = 200/(x-15)<BR>\n" );
document.write( "g = 200/(x-15) -2<BR>\n" );
document.write( "----------------------------<BR>\n" );
document.write( "Solve for \"g\":<BR>\n" );
document.write( "(400/x) -4 = (200/(x-15) -2<BR>\n" );
document.write( "Divide thru by 200 to get:<BR>\n" );
document.write( "(2/x) - 2/100 = (1/(x-15) - 1/100<BR>\n" );
document.write( "(2/x) - (1/(x-15) = 1/100<BR>\n" );
document.write( "200(x-15) - 100x = x(x-15)<BR>\n" );
document.write( "200x - 3000 - 100x = x^2-15x<BR>\n" );
document.write( "x^2 -115x +3000 = 0<BR>\n" );
document.write( "(x-75)(x-40) = 0<BR>\n" );
document.write( "----------------------------<BR>\n" );
document.write( "x is 75 or x = 40<BR>\n" );
document.write( "Need to solve for \"g\"<BR>\n" );
document.write( "g = 200/(x-15) -2<BR>\n" );
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document.write( "If x = 75, <BR>\n" );
document.write( "g = 200/(50) -2 = 2<BR>\n" );
document.write( "If x = 40,<BR>\n" );
document.write( "g = 200/25 - 2 = 6<BR>\n" );
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document.write( "Looks like original # of green is 2 or 6.<BR>\n" );
document.write( "Hummmm!!!<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
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document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );