document.write( "Question 1032286: I am three years older than my sister;our ages add up to 21 \n" ); document.write( "
Algebra.Com's Answer #646931 by Cromlix(4381)\"\" \"About 
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Hi there,
\n" ); document.write( "I am three years older than my sister;
\n" ); document.write( "our ages add up to 21
\n" ); document.write( "I = S + 3.......(1)
\n" ); document.write( "I + S = 21......(2)
\n" ); document.write( "Substitute (S + 3) for I
\n" ); document.write( "in Equation (2)
\n" ); document.write( "I + S = 21
\n" ); document.write( "(S + 3) + S = 21
\n" ); document.write( "S + 3 + S = 21
\n" ); document.write( "Collect like terms:
\n" ); document.write( "S + S = 21 - 3
\n" ); document.write( "2S = 18
\n" ); document.write( "S = 9
\n" ); document.write( "You are 12 years old
\n" ); document.write( "Your sister is 9 years old
\n" ); document.write( "Hope this helps :-) \n" ); document.write( "
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