document.write( "Question 454779: I travel 45 miles by car. It runs out of gas. I walk 3 miles. It takes me a total of 90 minutes. I travel 15 times faster in a car than walking. What is my driving speed. \n" ); document.write( "

Algebra.Com's Answer #312219 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
There are 2 different rates, so you need 2 different equations:
\n" ); document.write( "Let $\"+r+\"$ = driving speed
\n" ); document.write( "Let $\"+t+\"$ = time spent driving
\n" ); document.write( "In car:
\n" ); document.write( " $\"+d+=+r%2At+\"$
\n" ); document.write( "(1) $\"+45+=+r%2At+\"$
\n" ); document.write( "Walking:
\n" ); document.write( "(2) $\"+3+=+%28r%2F15%29%2A%281.5+-+t%29+\"$ ( units in miles, hrs, and miles/hr )
\n" ); document.write( "There are 2 equations and 2 unknowns, so it's solvable
\n" ); document.write( "(2) $\"+3+=+%28r%2F15%29%2A%281.5+-+t%29+\"$
\n" ); document.write( "(2) $\"+3+=+r%2F10+-+%281%2F15%29%2Ar%2At+\"$
\n" ); document.write( "Substitute (1) into (2)
\n" ); document.write( "(2) $\"+3+=+r%2F10+-+45%2F15+\"$
\n" ); document.write( "(2) $\"+3+=+r%2F10+-+3+\"$
\n" ); document.write( "(2) $\"+r%2F10+=+6+\"$
\n" ); document.write( "(2) $\"+r+=+60+\"$ mi/hr
\n" ); document.write( "check answer:
\n" ); document.write( "(1) $\"+45+=+r%2At+\"$
\n" ); document.write( "(1) $\"+t+=+45%2F60+\"$
\n" ); document.write( "(1) $\"+t+=+.75+\"$ hrs
\n" ); document.write( "and
\n" ); document.write( "(2) $\"+3+=+%2860%2F15%29%2A%281.5+-+.75%29+\"$
\n" ); document.write( "(2) $\"+3+=+4%2A.75+\"$
\n" ); document.write( "(2) $\"+3+=+3+\"$
\n" ); document.write( "OK \n" ); document.write( "

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