document.write( "Question 154191: Five years ago a man was seven times as old as his son. Five years hence, the father will be three times as old as his son. Find their present ages. \n" ); document.write( "

Algebra.Com's Answer #113502 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( " $\"f+-+5\"$ = father's age 5 years ago
\n" ); document.write( " $\"s+-+5\"$ = son's age 5 years ago
\n" ); document.write( " $\"f+-+5+=+7%2A%28s+-+5%29\"$
\n" ); document.write( " $\"f+-+5+=+7s+-+35\"$
\n" ); document.write( " $\"f+=+7s+-+30\"$
\n" ); document.write( "------------------
\n" ); document.write( " $\"f+%2B+5\"$ = father's age in 5 years hence
\n" ); document.write( " $\"s+%2B+5\"$ = son's age in 5 years hence
\n" ); document.write( " $\"f+%2B+5+=+3%2A%28s+%2B+5%29\"$
\n" ); document.write( " $\"f+%2B+5+=+3s+%2B+15\"$
\n" ); document.write( " $\"f+=+3s+%2B+10\"$
\n" ); document.write( "-----------------
\n" ); document.write( "Set the 2 expressions for $\"f\"$ equal to eachother
\n" ); document.write( " $\"7s+-+30+=+3s+%2B+10\"$
\n" ); document.write( " $\"4s+=+40\"$
\n" ); document.write( " $\"s+=+10\"$
\n" ); document.write( "Now substitute this in one of the equations
\n" ); document.write( " $\"f+=+7s+-+30\"$
\n" ); document.write( " $\"f+=+7%2A10+-+30\"$
\n" ); document.write( " $\"f+=+40\"$
\n" ); document.write( "The father is 40 and the son is 10
\n" ); document.write( " \n" ); document.write( "

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