document.write( "Question 88236: Three times a first number minus the second number is 20. The sum of the two numbers is 48. Find the two numbers. \n" ); document.write( "
Algebra.Com's Answer #64080 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
Let x=first #, y=second #\r
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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( " \"3%2Ax-1%2Ay=20\"
\n" ); document.write( " \"1%2Ax%2B1%2Ay=48\"
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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=20-3%2Ax\"Subtract \"3%2Ax\" from both sides
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\n" ); document.write( " \"y=%2820-3%2Ax%29%2F-1\" 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=-20%2B3%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"-20%2B3%2Ax\" we can substitute the expression \"-20%2B3%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%2B1%2Ahighlight%28%28-20%2B3%2Ax%29%29=48\" Replace y with \"-20%2B3%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"1%2Ax%2B1%2A%28-20%29%2B1%283%29x=48\" Distribute 1 to \"-20%2B3%2Ax\"
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\n" ); document.write( " \"1%2Ax-20%2B3%2Ax=48\" Multiply
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\n" ); document.write( " \"1%2Ax-20%2B3%2Ax=48\" Reduce any fractions
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\n" ); document.write( " \"1%2Ax%2B3%2Ax=48%2B20\"Add \"20\" to both sides
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\n" ); document.write( " \"1%2Ax%2B3%2Ax=68\" Combine the terms on the right side
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\n" ); document.write( " \"4%2Ax=68\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%281%2F4%29%284%2F1%29%29x=%2868%2F1%29%281%2F4%29\" Multiply both sides by \"1%2F4\". This will cancel out \"4%2F1\" and isolate x
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\n" ); document.write( " So when we multiply \"68%2F1\" and \"1%2F4\" (and simplify) we get
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\n" ); document.write( " \"x=17\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=17\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"1%2817%29%2B1%2Ay=48\" Plug in \"x=17\" into the 2nd equation
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\n" ); document.write( " \"17%2B1%2Ay=48\" Multiply
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\n" ); document.write( " \"1%2Ay=48-17\"Subtract \"17\" from both sides
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\n" ); document.write( " \"1%2Ay=31\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F1%29%281%29%29%2Ay=%2831%2F1%29%281%2F1%29\" Multiply both sides by \"1%2F1\". This will cancel out 1 on the left side.
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\n" ); document.write( " \"y=31%2F1\" Multiply the terms on the right side
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\n" ); document.write( " \"y=31\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=31\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=17\" and \"y=31\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"17\",\"31\")
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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( " \"3%2Ax-1%2Ay=20\"
\n" ); document.write( " \"1%2Ax%2B1%2Ay=48\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"3%2Ax-1%2Ay=20\" (red) and \"1%2Ax%2B1%2Ay=48\" (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 (\"17\",\"31\"). This verifies our answer.
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\n" ); document.write( " Check:
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\n" ); document.write( " Plug in (\"17\",\"31\") into the system of equations
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\n" ); document.write( " Let \"x=17\" and \"y=31\". Now plug those values into the equation \"3%2Ax-1%2Ay=20\"
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\n" ); document.write( " \"3%2A%2817%29-1%2A%2831%29=20\" Plug in \"x=17\" and \"y=31\"
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\n" ); document.write( " \"51-31=20\" Multiply
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\n" ); document.write( " \"20=20\" Add
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\n" ); document.write( " \"20=20\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"17\",\"31\") satisfies \"3%2Ax-1%2Ay=20\"
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\n" ); document.write( " Let \"x=17\" and \"y=31\". Now plug those values into the equation \"1%2Ax%2B1%2Ay=48\"
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\n" ); document.write( " \"1%2A%2817%29%2B1%2A%2831%29=48\" Plug in \"x=17\" and \"y=31\"
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\n" ); document.write( " \"17%2B31=48\" Multiply
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\n" ); document.write( " \"48=48\" Add
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\n" ); document.write( " \"48=48\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"17\",\"31\") satisfies \"1%2Ax%2B1%2Ay=48\"
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\n" ); document.write( " Since the solution (\"17\",\"31\") satisfies the system of equations
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\n" ); document.write( " \"3%2Ax-1%2Ay=20\"
\n" ); document.write( " \"1%2Ax%2B1%2Ay=48\"
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\n" ); document.write( " this verifies our answer.
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\n" ); document.write( "\n" ); document.write( "So the two numbers are 17 and 31
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