document.write( "Question 1039828: The Smiths are moving across the country. Mr. Smith leaves 4 hours before Mrs. Smith. If he averages 60 mph and she averages 80 mph, how long will it take Mrs. Smith to overtake Mr. Smith? \n" ); document.write( "

Algebra.Com's Answer #654577 by josmiceli(19441) $\"\"$ $\"About$

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How much of a head start in miles did Mr. Smith have?
\n" ); document.write( " $\"+d%5B1%5D+=+60%2A4+\"$
\n" ); document.write( " $\"+d%5B1%5D+=+240+\"$ mi
\n" ); document.write( "------------------
\n" ); document.write( "Start a stopwatch when Mrs. Smith leaves. Let $\"+t+\"$
\n" ); document.write( "= the time on the stopwatch in hrs when Mrs. Smith
\n" ); document.write( "catches up with Mr. Smith.
\n" ); document.write( "Let $\"+d+\"$ = the distance in miles that Mrs. Smith
\n" ); document.write( "travels until she overtakes Mr. Smith
\n" ); document.write( "------------------
\n" ); document.write( "Mr. Smith's equation:
\n" ); document.write( "(1) $\"+d+-+240+=+60t+\"$
\n" ); document.write( "Mrs. Smith's equation:
\n" ); document.write( "(2) $\"+d+=+80t+\"$
\n" ); document.write( "-------------------
\n" ); document.write( "Substitute (2) into (1)
\n" ); document.write( "(1) $\"+80t+-+240+=+60t+\"$
\n" ); document.write( "(1) $\"+20t+=+240+\"$
\n" ); document.write( "(1) $\"+t+=+12+\"$
\n" ); document.write( "Mrs. Smith overtakes Mr. Smith in 12 hrs
\n" ); document.write( "-------------------
\n" ); document.write( "check:
\n" ); document.write( "(2) $\"+d+=+80t+\"$
\n" ); document.write( "(2) $\"+d+=+80%2A12+\"$
\n" ); document.write( "(2) $\"+d+=+960+\"$ mi
\n" ); document.write( "and
\n" ); document.write( "(1) $\"+d+-+240+=+60t+\"$
\n" ); document.write( "(1) $\"+d+-+240+=+60%2A12+\"$
\n" ); document.write( "(1) $\"+d+=+240+%2B+720+\"$
\n" ); document.write( "(1) $\"+d+=+960+\"$ mi
\n" ); document.write( "OK \n" ); document.write( "

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