document.write( "Question 909148: the sum of the present age of the father and his daughter is 42 years, 7 years. later, the father will be 3 times old than the daughter. the present age of the father is \n" ); document.write( "

Algebra.Com's Answer #551638 by clearblueskai(22) $\"\"$ $\"About$

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let x =father's present age and y =daughter's present age
\n" ); document.write( " $\"x%2By=42\"$ - first equation\r
\n" ); document.write( "\n" ); document.write( "7 years later:
\n" ); document.write( "x+7 =father's age y+7=daughter's age
\n" ); document.write( " $\"x%2B7=3%28y%2B7%29\"$
\n" ); document.write( " $\"x%2B7=3y%2B21%29\"$ - second equation \r
\n" ); document.write( "\n" ); document.write( "use either elimination or substitution on the two equations
\n" ); document.write( "by substitution:
\n" ); document.write( " $\"x=42-y\"$
\n" ); document.write( " $\"%2842-y%29%2B7-3y-21=0\"$
\n" ); document.write( " $\"4y=28\"$
\n" ); document.write( " $\"y=7\"$
\n" ); document.write( " $\"x%2B%287%29=42\"$
\n" ); document.write( " $\"x=35\"$
\n" ); document.write( "Father's present age: 35
\n" ); document.write( " \n" ); document.write( "

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