document.write( "Question 984881: My son my father and I were all born on fathers day. When my son was born I was 3/7 the age of my father. Today my son is the age I was when he was born; in four years he will be exactly 1/3 the age of my father. how old was I when my son was born? \n" ); document.write( "
Algebra.Com's Answer #605810 by ankor@dixie-net.com(22740)\"\" \"About 
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My son my father and I were all born on fathers day.
\n" ); document.write( "Let y = your age
\n" ); document.write( "let f = father's age
\n" ); document.write( "let s = son's age
\n" ); document.write( ":
\n" ); document.write( " When my son was born I was 3/7 the age of my father.
\n" ); document.write( "y - s = \"3%2F7\"(f-s)
\n" ); document.write( "Multiply equation by 7
\n" ); document.write( "7(y - s) = 3(f - s)
\n" ); document.write( "7y - 7s = 3f - 3s
\n" ); document.write( "7y - 7s + 3s = 3f
\n" ); document.write( "7y - 4s = 3f
\n" ); document.write( ":
\n" ); document.write( " Today my son is the age I was when he was born;
\n" ); document.write( "s = \"1%2F2\"y
\n" ); document.write( "multiply equation by 2
\n" ); document.write( "2s = y
\n" ); document.write( ":
\n" ); document.write( "in four years he will be exactly 1/3 the age of my father.
\n" ); document.write( "s + 4 = \"1%2F3\"(f+4)
\n" ); document.write( "multiply equation by 3
\n" ); document.write( "3(s + 4) = f + 4
\n" ); document.write( "3s + 12 = f + 4
\n" ); document.write( "3s = f + 4 - 12
\n" ); document.write( "3s = f - 8
\n" ); document.write( ":
\n" ); document.write( "In the first equation, 7y - 4s = 3f, replace y with 2s
\n" ); document.write( "7(2s) - 4s = 3f
\n" ); document.write( "14s - 4s = 3f
\n" ); document.write( "10s = 3f
\n" ); document.write( "s = \"3%2F10\"f
\n" ); document.write( "we can write it
\n" ); document.write( "s = .3f
\n" ); document.write( ":
\n" ); document.write( "in the third equation, 3s = f - 8, replace s with .3f
\n" ); document.write( "3(.3f) = f - 8
\n" ); document.write( ".9f = f - 8
\n" ); document.write( "8 = f - .9f
\n" ); document.write( "8 = .1f
\n" ); document.write( "f = 8/.1
\n" ); document.write( "f = 80 yrs is Dad's age
\n" ); document.write( "then
\n" ); document.write( "s = .3f
\n" ); document.write( "s = .3(80)
\n" ); document.write( "s = 24 yrs is son's age
\n" ); document.write( "and
\n" ); document.write( "y - 2s
\n" ); document.write( "y = 2(24)
\n" ); document.write( "y = 48 yrs is his age
\n" ); document.write( ":
\n" ); document.write( "how old was I when my son was born? that would be 24 yrs ago
\n" ); document.write( "48 - 24 = 24yr old when your son was born
\n" ); document.write( " \n" ); document.write( "
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