document.write( "Question 563056: The sum of the digits of a certain two-digit number is 7. Reversing its digits increases the number by 9. What is the number?\r
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\n" ); document.write( "\n" ); document.write( "I do understand systems of equations. And although it appears quite simple, I can't understand how my second equation should be set up. So far I have: x + y = 7 \r
\n" ); document.write( "\n" ); document.write( "but I don't know how to mathematically express the term \"reversing it's digits\". FYI, the answer is 34. \n" ); document.write( "
Algebra.Com's Answer #364760 by htmentor(1343)\"\" \"About 
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The sum of the digits of a certain two-digit number is 7. Reversing its digits increases the number by 9. What is the number?
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\n" ); document.write( "Let t = the tens digit
\n" ); document.write( "Let u = the units digit
\n" ); document.write( "Then t + u = 7 -> t = 7 - u
\n" ); document.write( "The number, n, can be represented as n = 10t + u = 10(7-u) + u = 70 - 9u
\n" ); document.write( "When the digits are reversed we have:
\n" ); document.write( "n + 9 = 10u + t = 10u + (7-u) = 9u + 7 -> n = 9u - 2
\n" ); document.write( "So we have two equations and two unknowns:
\n" ); document.write( "n = 70 - 9u
\n" ); document.write( "n = -2 + 9u
\n" ); document.write( "Adding the two equations gives
\n" ); document.write( "2n = 68
\n" ); document.write( " n = 34
\n" ); document.write( "So the number is 34
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