document.write( "Question 884870: after five year, the age of a father will be thrice the age of his son, whereas five years ago, he was seven times old as his son was. What is father's present age? \n" ); document.write( "

Algebra.Com's Answer #534716 by JulietG(1812) $\"\"$ $\"About$

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F + 5 = 3(S+5)
\n" ); document.write( "F - 5 = 7(S-5)
\n" ); document.write( ".
\n" ); document.write( "The easiest way to do this problem is to isolate S. We'll do that by finding the value of F and substituting.
\n" ); document.write( "F + 5 = 3(S+5)
\n" ); document.write( "Subtract 5 from each side.
\n" ); document.write( "F = 3S + 15 - 5
\n" ); document.write( "F = 3S + 10
\n" ); document.write( "Now take that value of F and put it into the second equation.
\n" ); document.write( "F - 5 = 7(S-5)
\n" ); document.write( "(3S+10)-5=7S-35
\n" ); document.write( "3S+5 = 7S - 35
\n" ); document.write( "Subtract 3S from each side
\n" ); document.write( "5 = 4S - 35
\n" ); document.write( "Add 35 to each side
\n" ); document.write( "40 = 4S
\n" ); document.write( "Divide each side by 4
\n" ); document.write( "10 = S
\n" ); document.write( ".
\n" ); document.write( "If the son is 10, then in five years, the son will be 15. The father will then be 3 times that, or 45. If he is 45 in 5 years, then he is 40 now.
\n" ); document.write( "Let's check by working the second half.
\n" ); document.write( "\"five years ago, he was seven times old as his son was. \"
\n" ); document.write( "Five years ago, the son was 5. Five years ago, the father was 35.
\n" ); document.write( "That is indeed seven times the age.
\n" ); document.write( "Success! \n" ); document.write( "

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