document.write( "Question 108858: Two numbers have a sum of 39. Their difference is 11. What are the two numbers? Yes this is third grade math. \n" ); document.write( "
Algebra.Com's Answer #79378 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
The expression \"Two numbers have a sum of 39\" is written as\r
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\n" ); document.write( "\n" ); document.write( "\"x%2By=39\"\r
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\n" ); document.write( "\n" ); document.write( "and \"Their difference is 11\" is written as\r
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\n" ); document.write( "\n" ); document.write( "\"x-y=11\"\r
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\n" ); document.write( "\n" ); document.write( "So we get the system \r
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\n" ); document.write( "\n" ); document.write( "\"x%2By=39\"
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Solved by pluggable solver: Solving a linear system of equations by subsitution

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\n" ); document.write( " Lets start with the given system of linear equations
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\n" ); document.write( " \"1%2Ax%2B1%2Ay=39\"
\n" ); document.write( " \"1%2Ax-1%2Ay=11\"
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\n" ); document.write( " Now in order to solve this system by using substitution, we need to solve (or isolate) one variable. I'm going to choose y.
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\n" ); document.write( " Solve for y for the first equation
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\n" ); document.write( " \"1%2Ay=39-1%2Ax\"Subtract \"1%2Ax\" from both sides
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\n" ); document.write( " \"y=%2839-1%2Ax%29\" Divide both sides by 1.
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\n" ); document.write( " Which breaks down and reduces to
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\n" ); document.write( " \"y=39-1%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"39-1%2Ax\" we can substitute the expression \"39-1%2Ax\" into y of the 2nd equation. This will eliminate y so we can solve for x.
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\n" ); document.write( " \"1%2Ax%2B-1%2Ahighlight%28%2839-1%2Ax%29%29=11\" Replace y with \"39-1%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"1%2Ax-1%2A%2839%29-1%28-1%29x=11\" Distribute -1 to \"39-1%2Ax\"
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\n" ); document.write( " \"1%2Ax-39%2B1%2Ax=11\" Multiply
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\n" ); document.write( " \"1%2Ax-39%2B1%2Ax=11\" Reduce any fractions
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\n" ); document.write( " \"1%2Ax%2B1%2Ax=11%2B39\"Add \"39\" to both sides
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\n" ); document.write( " \"1%2Ax%2B1%2Ax=50\" Combine the terms on the right side
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\n" ); document.write( " \"2%2Ax=50\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%281%2F2%29%282%2F1%29%29x=%2850%2F1%29%281%2F2%29\" Multiply both sides by \"1%2F2\". This will cancel out \"2%2F1\" and isolate x
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\n" ); document.write( " So when we multiply \"50%2F1\" and \"1%2F2\" (and simplify) we get
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\n" ); document.write( " \"x=25\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=25\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"1%2825%29-1%2Ay=11\" Plug in \"x=25\" into the 2nd equation
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\n" ); document.write( " \"25-1%2Ay=11\" Multiply
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\n" ); document.write( " \"-1%2Ay=11-25\"Subtract \"25\" from both sides
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\n" ); document.write( " \"-1%2Ay=-14\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F-1%29%28-1%29%29%2Ay=%28-14%2F1%29%281%2F-1%29\" Multiply both sides by \"1%2F-1\". This will cancel out -1 on the left side.
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\n" ); document.write( " \"y=-14%2F-1\" Multiply the terms on the right side
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\n" ); document.write( " \"y=14\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=14\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=25\" and \"y=14\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"25\",\"14\")
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\n" ); document.write( " Notice if we graph the equations (if you need help with graphing, check out this solver)
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\n" ); document.write( " \"1%2Ax%2B1%2Ay=39\"
\n" ); document.write( " \"1%2Ax-1%2Ay=11\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"1%2Ax%2B1%2Ay=39\" (red) and \"1%2Ax-1%2Ay=11\" (green) (hint: you may have to solve for y to graph these) intersecting at the blue circle.
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\n" ); document.write( " and we can see that the two equations intersect at (\"25\",\"14\"). This verifies our answer.
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\n" ); document.write( " Check:
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\n" ); document.write( " Plug in (\"25\",\"14\") into the system of equations
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\n" ); document.write( " Let \"x=25\" and \"y=14\". Now plug those values into the equation \"1%2Ax%2B1%2Ay=39\"
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\n" ); document.write( " \"1%2A%2825%29%2B1%2A%2814%29=39\" Plug in \"x=25\" and \"y=14\"
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\n" ); document.write( " \"25%2B14=39\" Multiply
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\n" ); document.write( " \"39=39\" Add
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\n" ); document.write( " \"39=39\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"25\",\"14\") satisfies \"1%2Ax%2B1%2Ay=39\"
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\n" ); document.write( " Let \"x=25\" and \"y=14\". Now plug those values into the equation \"1%2Ax-1%2Ay=11\"
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\n" ); document.write( " \"1%2A%2825%29-1%2A%2814%29=11\" Plug in \"x=25\" and \"y=14\"
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\n" ); document.write( " \"25-14=11\" Multiply
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\n" ); document.write( " \"11=11\" Add
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\n" ); document.write( " \"11=11\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"25\",\"14\") satisfies \"1%2Ax-1%2Ay=11\"
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\n" ); document.write( " Since the solution (\"25\",\"14\") satisfies the system of equations
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\n" ); document.write( " \"1%2Ax%2B1%2Ay=39\"
\n" ); document.write( " \"1%2Ax-1%2Ay=11\"
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\n" ); document.write( " this verifies our answer.
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