document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=644763>Question 644763</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Hey guys would be great if you could help me out with the following problem:<BR>\n" );
document.write( "4-digit code with 0-9 as possible digits. How many codes are there that<BR>\n" );
document.write( "contain the digit \"0\" exactly twice?<BR>\n" );
document.write( "I found that (10^4) - (9^4) = 3439 which is the number of codes with \"0\" at least once. Any help on how I would go about solving two instances of \"0\" would be awesome.<BR>\n" );
document.write( "Thanks,<BR>\n" );
document.write( "Rob </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #405246 by </B><A HREF=/tutors/aboutme.mpl?userid=josmiceli><B>josmiceli(19441)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=josmiceli><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/cgi-bin/show-face.mpl?user=josmiceli><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=405246\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> the codes will look like one of these:<BR>\n" );
document.write( "00xx<BR>\n" );
document.write( "xx00<BR>\n" );
document.write( "0x0x<BR>\n" );
document.write( "x0x0<BR>\n" );
document.write( "x00x<BR>\n" );
document.write( "0xx0 <BR>\n" );
document.write( "where the x's can't be 0, but <BR>\n" );
document.write( "they can be 1-9<BR>\n" );
document.write( "-------------<BR>\n" );
document.write( "So there are <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+9%5E2+=+81+ ALIGN=MIDDLE  ALT=\"+9%5E2+=+81+\"   DISABLED_style= \"max-width:90%; height:auto;\" > possible<BR>\n" );
document.write( "codes for each of these 6 choices<BR>\n" );
document.write( "there are 6*81 = 486 possible<BR>\n" );
document.write( "codes altogether </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );