document.write( "Question 242993: My car gets 25 mpg for in-town driving, and 40 mpg on the highway. If I used 51 gallons on a recent 1800 mile trip, how many miles were highway miles? \n" ); document.write( "

Algebra.Com's Answer #178005 by Theo(13342) $\"\"$ $\"About$

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t = town miles
\n" ); document.write( "c = country miles
\n" ); document.write( "t + c = 1800\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "t/24 + c/40 = 51 gallons.
\n" ); document.write( "multiply both sides of equation by 24*40 to get:
\n" ); document.write( "40*t + 24*c = 51*40*24
\n" ); document.write( "this becomes:
\n" ); document.write( "40t + 24c = 48960\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "t + c = 1800
\n" ); document.write( "subtract c from both sides of equation to get:
\n" ); document.write( "t = 1800-c\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "substitute 1800-c for t in first equation to get:
\n" ); document.write( "40*(1800-c) + 24c = 48960
\n" ); document.write( "simplify to get:
\n" ); document.write( "72000 - 40c + 24c = 48960
\n" ); document.write( "subtract 48960 from both sides of equation and add 40c to both sides of equation and subtract 24c from both sides of equation to get:
\n" ); document.write( "16c = 23040
\n" ); document.write( "divide both sides of equation by 16 to get
\n" ); document.write( "c = 1440\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "solve for t from c + t = 1800 to get:
\n" ); document.write( "t = 1800 - 1440 = 360\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "replace t with 360 and c with 1440 in gallons equation to get:
\n" ); document.write( "360/24 + 1440/40 = 15 + 36 = 51 gallons.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "you drove 360 town miles and 1440 country miles.\r
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "

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