document.write( "Question 890621: A car travel 15KM in a city at a certain speed. outside the city it travel 72KM at twice the former speed. if the total traveling time is 1h 8min, find the average speed in the city \n" ); document.write( "

Algebra.Com's Answer #539114 by ankor@dixie-net.com(22740) $\"\"$ $\"About$

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A car travel 15KM in a city at a certain speed.
\n" ); document.write( " outside the city it travel 72KM at twice the former speed.
\n" ); document.write( " if the total traveling time is 1h 8min, find the average speed in the city
\n" ); document.write( ":
\n" ); document.write( "let s = speed in the city
\n" ); document.write( "then 2s = speed in the country
\n" ); document.write( ":
\n" ); document.write( "change 1 hr 8 min to $\"68%2F60\"$ reduces to $\"17%2F15\"$ hrs
\n" ); document.write( ":
\n" ); document.write( "Write a time equation; time = dist/speed
\n" ); document.write( ":
\n" ); document.write( "City time + country time = 1 hr 8min
\n" ); document.write( " $\"15%2Fs\"$ + $\"72%2F%282s%29\"$ = $\"17%2F15\"$
\n" ); document.write( "multiply equation by 30s
\n" ); document.write( "30s* $\"15%2Fs\"$ + 30s* $\"72%2F%282s%29\"$ = 30s* $\"17%2F15\"$
\n" ); document.write( "cancel the denominators and you have
\n" ); document.write( "30(15) + 15(72) = 2s(17)
\n" ); document.write( "450 + 1080 = 34s
\n" ); document.write( "1530 = 34s
\n" ); document.write( "s = 1530/34
\n" ); document.write( "s = 45 km/h in the city
\n" ); document.write( ":
\n" ); document.write( ":
\n" ); document.write( "Check this by finding the time at each speed, (90 km/h in the country)
\n" ); document.write( "15/45 = .333 hrs
\n" ); document.write( "72/90 = .8 hrs
\n" ); document.write( "---------------
\n" ); document.write( "total = 1.133 hrs which is 6 hr 8 min \n" ); document.write( "

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