document.write( "Question 597196: The sum of three numbers is 4. The first number minus the second plus 5 times the third is
\n" ); document.write( "20. The third plus 5 times the first plus the second is -8. Find the numbers.
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Algebra.Com's Answer #378084 by math-vortex(648)\"\" \"About 
You can put this solution on YOUR website!
Hi, there--\r
\n" ); document.write( "\n" ); document.write( "To solve this problem, we define variables for each number. Then we create a system of three equations in three variables. Finally, we solve the system of equations to find the three numbers.
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\n" ); document.write( "[I] Define the variables.\r
\n" ); document.write( "\n" ); document.write( "Call the first number a.
\n" ); document.write( "Call the second number b.
\n" ); document.write( "Call the third number c.
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\n" ); document.write( "[II] Create three equations.
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\n" ); document.write( "The sum of the three numbers is 4. Using algebra, we write this relationship as
\n" ); document.write( "\"a%2Bb%2Bc=4\"
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\n" ); document.write( "The first number minus the second plus 5 times the third is
\n" ); document.write( "20. In algebra we write this relationship as
\n" ); document.write( "\"a-b%2B5c=20\"
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\n" ); document.write( "The third plus 5 times the first plus the second is -8. In algebra we write this relationship as
\n" ); document.write( "\"c%2B5a%2Bb=-8\"
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\n" ); document.write( "Rewrite the third equation to have the variables in alphabetical order.
\n" ); document.write( "\"5a%2Bb%2Bc=-8\"
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\n" ); document.write( "[III] Solve the system of equation.
\n" ); document.write( "I'll use the elimination and substitution methods here. You can also use a matrix to easily solve the system. Email me at my gmail address below if you want to see the matrix method, or repost this problem and ask for a matrix method solution.
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\n" ); document.write( "\"a%2Bb%2Bc=4\"
\n" ); document.write( "\"a-b%2B5c=20\"
\n" ); document.write( "\"5a%2Bb%2Bc=-8\"
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\n" ); document.write( "Add the 1st and 2nd equations together; solve to give an equation in a and c (NOTE: b+(-b)=0.)
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\n" ); document.write( "Subtract \"6a%2B6c=12\" from \"2a%2B6c=24\". Solve for a.
\n" ); document.write( "\"-4a=12\"
\n" ); document.write( "\"a=-3\"
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\n" ); document.write( "Substitute -3 for a in \"2a%2B6c=24\". Solve for c.
\n" ); document.write( "\"2%28-3%29%2B6c=24\"
\n" ); document.write( "\"%28-6%29%2B6c=24\"
\n" ); document.write( "\"6c=30\"
\n" ); document.write( "\"c=5\"
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\n" ); document.write( "Substitute -3 for a and 5 for c in the first equation. Solve for b.
\n" ); document.write( "\"a%2Bb%2Bc=4\"
\n" ); document.write( "\"%28-3%29%2Bb%2B%285%29=4\"
\n" ); document.write( "\"2%2Bb=4\"
\n" ); document.write( "\"b=2\"
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\n" ); document.write( "According to our algebra, the three numbers are -3, 2, and 5.
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\n" ); document.write( "[IV] Check your work.
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\n" ); document.write( "\"a%2Bb%2Bc=4\"
\n" ); document.write( "\"%28-3%29%2B2%2B5=4\"
\n" ); document.write( "\"4=4\"
\n" ); document.write( "Check!
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\n" ); document.write( "\"a-b%2B5c=20\"
\n" ); document.write( "\"%28-3%29-2%2B5%285%29=20\"
\n" ); document.write( "\"-5%2B25=20\"
\n" ); document.write( "\"20=20\"
\n" ); document.write( "Bingo!
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\n" ); document.write( "\"c%2B5a%2Bb=-8\"
\n" ); document.write( "\"%285%29%2B5%28-3%29%2B%282%29=-8\"
\n" ); document.write( "\"5-15%2B2=-8\"
\n" ); document.write( "\"-8=-8\"
\n" ); document.write( "Presto!
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\n" ); document.write( "That's it! Feel free to email me via gmail with any questions about the solution.
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\n" ); document.write( "Ms.Figgy
\n" ); document.write( "math.in.the.vortex@gmail.com
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