document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=673004>Question 673004</A>: <I><SPAN STYLE=\"word-break: break-all;\"> In a mixed class, there are 10 girls. <BR>\n" );
document.write( "If 2 pupils are selected at random, the probability that they are both girls is 0.15<BR>\n" );
document.write( "How many boys are in the class?<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #418430 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=418430\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> In a mixed class, there are 10 girls. <BR>\n" );
document.write( "If 2 pupils are selected at random, the probability that they are both girls is 0.15<BR>\n" );
document.write( "How many boys are in the class?\r<BR>\n" );
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document.write( "Let # of boys be \"x\".<BR>\n" );
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document.write( "0.15 = 10C2/(10+x)C2<BR>\n" );
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document.write( "0.15 = (45)/[(10+x)(9+x)]/2<BR>\n" );
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document.write( "0.15 = 90/[(10+x)(9+x)]<BR>\n" );
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document.write( "1/600 = 1/[(10+x)(9+x)]<BR>\n" );
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document.write( "(10+x)(9+x) = 600<BR>\n" );
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document.write( "x^2+19x+90 = 600<BR>\n" );
document.write( "----<BR>\n" );
document.write( "x^2 + 19x - 510 = 0<BR>\n" );
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document.write( "Factor:<BR>\n" );
document.write( "(x-15)(x+34) = 0<BR>\n" );
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document.write( "Positive solution:<BR>\n" );
document.write( "x = 15 (# of boys in the class)<BR>\n" );
document.write( "=====================================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
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