document.write( "Question 193820: Isaac is nine years older than Kylie. Isaac is four times as old as Brian was three years ago. Brian is eighteen years younger than Isaac. How old is Kylie? \n" ); document.write( "

Algebra.Com's Answer #145541 by josmiceli(19441) $\"\"$ $\"About$

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Let $\"I\"$ = Isaac's age now
\n" ); document.write( "Let $\"K\"$ = Kylie's age now
\n" ); document.write( "Let $\"B\"$ = Brian's age now
\n" ); document.write( "given:
\n" ); document.write( "(1) $\"I+=+K+%2B+9\"$
\n" ); document.write( " $\"B+-+3\"$ = Brian's age 3 years ago
\n" ); document.write( "(2) $\"I+=+4%2A%28B+-+3%29\"$
\n" ); document.write( "(3) $\"B+=+I+-+18\"$
\n" ); document.write( "-------------------
\n" ); document.write( "I have 3 equations and 3 unknowns,
\n" ); document.write( "so it is solvable
\n" ); document.write( "Substitute (2) in (3)
\n" ); document.write( "(3) $\"B+=+I+-+18\"$
\n" ); document.write( "(3) $\"B+=+4%2A%28B+-+3%29+-+18\"$
\n" ); document.write( "(3) $\"B+=+4B+-+12+-+18\"$
\n" ); document.write( "(3) $\"3B+=+30\"$
\n" ); document.write( " $\"B+=+10\"$
\n" ); document.write( "And from (2):
\n" ); document.write( "(2) $\"I+=+4%2A%2810+-+3%29\"$
\n" ); document.write( "(2) $\"I+=+4%2A7\"$
\n" ); document.write( "(2) $\"I+=+28\"$
\n" ); document.write( "And from (1):
\n" ); document.write( "(1) $\"28+=+K+%2B+9\"$
\n" ); document.write( "(1) $\"K+=+19\"$
\n" ); document.write( "Kylie is 19
\n" ); document.write( "check answer:
\n" ); document.write( "Is Isaac nine years older than Kylie? Yes
\n" ); document.write( "Is Brian eighteen years younger than Isaac? Yes
\n" ); document.write( "Is Isaac four times as old as Brian was three years ago? Yes \n" ); document.write( "

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