document.write( "Question 206084: Could you please help me understand how I would check for divisibility by 45. \r
\n" ); document.write( "\n" ); document.write( "I thought you would first check for divisibility of 5 in the number and then I thought if you added the numbers together and they combined to give you a total of 9 then the number would be divisible by 45 but this worked for a lot of numbers I tried but then I tried 31120110 and it is not divisible by 45 so that puts my theory out.
\n" ); document.write( "Could you explain how I would check for divisibility of 45. \r
\n" ); document.write( "\n" ); document.write( "Many thanks \n" ); document.write( "

Algebra.Com's Answer #155639 by jim_thompson5910(35256) $\"\"$ $\"About$

You can put this solution on YOUR website!
To check if a number is divisible by 45, you are correct: you check to see if it is divisible by both 5 and 9. Since the last digit of 31120110 is a 0, this means that it is divisible by 5. Because the digits add up to 9 (3+1+1+2+0+1+1+0=9), this means that the number is also divisible by 9. So this means that 31120110 is indeed divisible by 45. \r
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\n" ); document.write( "\n" ); document.write( "Note: as a check, $\"31120110%2F9=691558\"$ which confirms our answer.\r
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\n" ); document.write( "\n" ); document.write( "Note: this theory works for any composite number. For instance, the divisibility rule for 6 states that any number is divisible by 6 if it is both divisible by 2 and 3 (which multiply to 6). \n" ); document.write( "

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