document.write( "Question 826820: Sarah's age is 1/3 of her father's age. In 13 years time her age will be 1/2 of her father's age. How old is Sarah now? \n" ); document.write( "

Algebra.Com's Answer #498278 by josmiceli(19441) $\"\"$ $\"About$

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Let $\"+s+\"$ = Sarah's age now
\n" ); document.write( "Let $\"+f+\"$ = father's age now
\n" ); document.write( " $\"+s+%2B+13+\"$ = Sarah's age in 13 yrs
\n" ); document.write( " $\"+f+%2B+13+\"$ = father's age in 13 yrs
\n" ); document.write( "----------------------------------------
\n" ); document.write( "(1) $\"+s+=+%281%2F3%29%2Af+\"$
\n" ); document.write( "(2) $\"+s+%2B+13+=+%281%2F2%29%2A%28f+%2B+13%29+\"$
\n" ); document.write( "--------------------------------------
\n" ); document.write( "(1) $\"+3s+=+f+\"$
\n" ); document.write( "(2) $\"+2%2A%28s+%2B+13%29+=+f+%2B+13+\"$
\n" ); document.write( "(2) $\"+2s+%2B+26++=+f+%2B+13+\"$
\n" ); document.write( "(2) $\"+f+-+2s+=+13+\"$
\n" ); document.write( "--------------------------
\n" ); document.write( "Substitute (1) into (2)
\n" ); document.write( "(2) $\"+3s+-+2s+=+13+\"$
\n" ); document.write( "(2) $\"+s+=+13+\"$
\n" ); document.write( "Sarah is 13 now
\n" ); document.write( "and, since
\n" ); document.write( "(1) $\"+3s+=+f+\"$
\n" ); document.write( "(1) $\"+3%2A13+=+f+\"$
\n" ); document.write( "(1) $\"+f+=+39+\"$
\n" ); document.write( "check:
\n" ); document.write( "(2) $\"+s+%2B+13+=+%281%2F2%29%2A%28f+%2B+13%29+\"$
\n" ); document.write( "(2) $\"+13+%2B+13+=+%281%2F2%29%2A%2839+%2B+13%29+\"$
\n" ); document.write( "(2) $\"+26+=+%281%2F2%29%2A52+\"$
\n" ); document.write( "(2) $\"+26+=+26+\"$
\n" ); document.write( "OK\r
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "

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