document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=28412>Question 28412</A>: <I><SPAN STYLE=\"word-break: break-all;\"> how do you figure out the factors of a number and how do you know if it is prime or not? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #15445 by </B><A HREF=/tutors/aboutme.mpl?userid=longjonsilver><B>longjonsilver(2297)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=longjonsilver><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=longjonsilver><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=15445\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <b>Primes</b><BR>\n" );
document.write( "Any number can be written as a set of prime numbers multiplied together. You need to know the first few primes... 2,3,5,7,11,13,... The majority of work in this area will give you numbers that factorise into these numbers. Higher primes are too much work for students in exam conditions.\r<BR>\n" );
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document.write( "<b>FACTOR of 2</b>:<BR>\n" );
document.write( "Is it even? if so, 2 is a factor eg 236 --> 2*118\r<BR>\n" );
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document.write( "<b>FACTOR of 3</b>:<BR>\n" );
document.write( "When you add up the digits, is that number divisible by 3? If so, the original number has 3 as a factor eg 351 --> 3+5+1=9 and 3 goes into 9, so 351 --> 3*117\r<BR>\n" );
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document.write( "<b>FACTOR of 5</b>:<BR>\n" );
document.write( "Is the last digit a 5 or a 0? If so, 5 is a factor eg 235 --> 5*47.\r<BR>\n" );
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document.write( "<b>Example</b>:<BR>\n" );
document.write( "Write 27027 as a set of factors.\r<BR>\n" );
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document.write( "Method:<BR>\n" );
document.write( "Start with 2, the look for 3 then 5 and keep keep working at the number with ever increasing primes:\r<BR>\n" );
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document.write( "The number is odd, so 2 is not a factor.\r<BR>\n" );
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document.write( "Add up the digits: 2+7+0+2+7=18 --> 18 divides by 3 so 3 is a factor --> 3*9009\r<BR>\n" );
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document.write( "Now look at 9009 --> 9+0+0+9 = 18 which again divides by 3, so we have 3*3*3003\r<BR>\n" );
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document.write( "Similar process... 3*3*3*1001\r<BR>\n" );
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document.write( "Now 1+0+0+1=2... and 2 does not divide by 3. \r<BR>\n" );
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document.write( "So lets move onto 5. last digit is not 5 or 0 so 5 is not a factor. \r<BR>\n" );
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document.write( "How about 7? Divide it and see. Yes --> 3*3*3*7*143\r<BR>\n" );
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document.write( "143/7? No, \r<BR>\n" );
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document.write( "So next is 11. Yes --> 3*3*3*7*11*13\r<BR>\n" );
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document.write( "Finally 13 is a prime so that is it. Final answer is 3*3*3*7*11*13.\r<BR>\n" );
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document.write( "jon. </SPAN>\n" );
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