document.write( "Question 720620: if today a father is four times as old as his son and five years ago he was five times as old as his son, find their present age \n" ); document.write( "

Algebra.Com's Answer #441899 by josmiceli(19441) $\"\"$ $\"About$

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Let $\"+f+\"$ = Father's age now
\n" ); document.write( "Let $\"+s+\"$ = Son's age now
\n" ); document.write( "given:
\n" ); document.write( "(1) $\"+f+=+4s+\"$
\n" ); document.write( "(2) $\"+f+-+5+=+5%2A%28+s+-+5+%29+\"$
\n" ); document.write( "----------------------
\n" ); document.write( "(2) $\"+f+-+5+=+5s+-+25+\"$
\n" ); document.write( "(2) $\"+5s+-+f+=+20+\"$
\n" ); document.write( "By substitution:
\n" ); document.write( "(2) $\"+5s+-+4s+=+20+\"$
\n" ); document.write( " $\"+s+=+20+\"$
\n" ); document.write( "and
\n" ); document.write( "(1) $\"+f+=+4s+\"$
\n" ); document.write( "(1) $\"+f+=+4%2A20+\"$
\n" ); document.write( "(1) $\"+f+=+80+\"$
\n" ); document.write( "The Father is 80
\n" ); document.write( "The Son is 20
\n" ); document.write( "--------------
\n" ); document.write( "check:
\n" ); document.write( "5 years ago, the Father was $\"+75+\"$
\n" ); document.write( "5 years ago, the Son was $\"+15+\"$
\n" ); document.write( " $\"+75+=+5%2A15+\"$
\n" ); document.write( " $\"+75+=+75+\"$
\n" ); document.write( "OK
\n" ); document.write( " \n" ); document.write( "

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