document.write( "Question 936399: 5 years ago Christian was twice as old as Alec. The sum of their ages in 6 years will be 40 years. What is the present age of each?
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Algebra.Com's Answer #569854 by srinivas.g(540)\"\" \"About 
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let x, y be the current ages of Christian, Alec
\n" ); document.write( "5 years ago Christian was twice as old as Alec.
\n" ); document.write( " x-5 = 2*(y-5)
\n" ); document.write( " x-5 =2*y+2*(-5)
\n" ); document.write( " x-5 =2y-10
\n" ); document.write( " move 2y to the left
\n" ); document.write( " x-2y-5 = -10
\n" ); document.write( " move -5 to the right
\n" ); document.write( " x-2y =-10+5
\n" ); document.write( " x-2y =-5 ................eq(1)
\n" ); document.write( " The sum of their ages in 6 years will be 40 years
\n" ); document.write( " (x+6)+(y+6)=40
\n" ); document.write( " x+y+12 =40
\n" ); document.write( " x+y= 40-12
\n" ); document.write( " x+y= 28 -----------eq(2)\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "\n" ); document.write( "
Solved by pluggable solver: SOLVE linear system by SUBSTITUTION
Solve:
\n" ); document.write( " \"+system%28+%0D%0A++++1%5Cx+%2B+-2%5Cy+=+-5%2C%0D%0A++++1%5Cx+%2B+1%5Cy+=+28+%29%0D%0A++\"We'll use substitution. After moving -2*y to the right, we get:
\n" ); document.write( " \"1%2Ax+=+-5+-+-2%2Ay\", or \"x+=+-5%2F1+-+-2%2Ay%2F1\". Substitute that
\n" ); document.write( " into another equation:
\n" ); document.write( " \"1%2A%28-5%2F1+-+-2%2Ay%2F1%29+%2B+1%5Cy+=+28\" and simplify: So, we know that y=11. Since \"x+=+-5%2F1+-+-2%2Ay%2F1\", x=17.
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\n" ); document.write( " Answer: \"system%28+x=17%2C+y=11+%29\".
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