document.write( "Question 393236: 10. A motorist covered a journey of 690 km in 8 hours. He covered part of the journey at 90 km/h and the rest at 80 km/h.What was the distance that he covered at 80 km/h? \n" ); document.write( "

Algebra.Com's Answer #279119 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
Let $\"d\"$ = the distance covered at 80 km/hr
\n" ); document.write( "Then $\"690+-+d\"$ = distance covered at 90 km/hr
\n" ); document.write( "Let $\"t\"$ = the time in hrs driven at 80 kmm/hr
\n" ); document.write( "The $\"8+-+t\"$ = time in hrs driven at 90 km/hr
\n" ); document.write( "I can write 2 equations:
\n" ); document.write( "(1) $\"d+=+80t\"$
\n" ); document.write( "(2) $\"690+-+d+=+90%2A%288+-+t%29\"$
\n" ); document.write( "-----------------------
\n" ); document.write( "From (1):
\n" ); document.write( " $\"t+=+d%2F80\"$
\n" ); document.write( "and, substituting:
\n" ); document.write( "(2) $\"690+-+d+=+90%2A%288+-+d%2F80%29\"$
\n" ); document.write( " $\"690+-+d+=+720+-+%289%2F8%29%2Ad\"$
\n" ); document.write( " $\"5520+-+8d+=+5760+-+9d\"$
\n" ); document.write( " $\"d+=+240\"$
\n" ); document.write( " The distance that he covered at 80 km/hr was 240 km
\n" ); document.write( "check:
\n" ); document.write( " $\"t+=+d%2F80\"$
\n" ); document.write( " $\"t+=+240%2F80\"$
\n" ); document.write( " $\"t+=+3\"$ hrs
\n" ); document.write( "(2) $\"690+-+d+=+90%2A%288+-+3%29\"$
\n" ); document.write( " $\"690+-+240+=+90%2A5\"$
\n" ); document.write( " $\"450+=+450\"$
\n" ); document.write( "OK \n" ); document.write( "

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