document.write( "Question 174973: I need help!!
\n" ); document.write( "- A car travelled 470 km from Sudbury to Brandford in 5 hours. For part of the trip, the car travelled at 100 km/h. For the rest of the trip, it travelled at 90 km/h. How far did the car travel at each speed?\r
\n" ); document.write( "\n" ); document.write( "I tried
\n" ); document.write( "x+y=5
\n" ); document.write( "100x+90=470\r
\n" ); document.write( "\n" ); document.write( "100x+100y=500
\n" ); document.write( "100x+90y=470\r
\n" ); document.write( "\n" ); document.write( "= 10y = 30
\n" ); document.write( "x=2 y=3
\n" ); document.write( "but I only got half marks. Where did I go wrong and what was the answer?
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Algebra.Com's Answer #130041 by Electrified_Levi(103)\"\" \"About 
You can put this solution on YOUR website!
Hi, Hope I can help,
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\n" ); document.write( "I need help!!
\n" ); document.write( "- A car travelled 470 km from Sudbury to Brandford in 5 hours. For part of the trip, the car travelled at 100 km/h. For the rest of the trip, it travelled at 90 km/h. How far did the car travel at each speed?
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\n" ); document.write( "We will start fresh
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\n" ); document.write( "First we need to know a formula
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\n" ); document.write( "\"+%28rate%29%28time%29=+distance+\", or with abbreviations, \"+r%29%28t%29+=+d+\"
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\n" ); document.write( "A car travelled 470 km from Sudbury to Brandford in 5 hours. For part of the trip, the car travelled at 100 km/h. For the rest of the trip, it travelled at 90 km/h. How far did the car travel at each speed?
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\n" ); document.write( "This problem is a little tricky, since the car is going two speeds, instead of just one, we also have two different times.
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\n" ); document.write( "This will mean we will have two unknowns, we can find the other unknowns with the information we have
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\n" ); document.write( "A car travelled 470 km from Sudbury to Brandford in 5 hours. For part of the trip, the car travelled at 100 km/h. For the rest of the trip, it travelled at 90 km/h. How far did the car travel at each speed?
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\n" ); document.write( "Remember that \"+rate%28time%29+=+distance+\", we don't know the time or distance for either one of the speeds, but we know the total distance and total time
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\n" ); document.write( "We can say that the time it took when the car went 90 km/h, the time it took would be \"+x+\"
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\n" ); document.write( "We can say that how long it took when the car went 100 km/h, the time it took would be \"+5+-+x+\", ( if you subtract the other time, from the total time, you will find the second unknown time )
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\n" ); document.write( "It is the same concept with the distances
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\n" ); document.write( "one distance would be \"+y+\"
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\n" ); document.write( "the second unknown distance would be \"+470+-+y+\"
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\n" ); document.write( "We can now find equations to this problem
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\n" ); document.write( "\"+r%28t%29+=+d+\"
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\n" ); document.write( "Equation 1
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\n" ); document.write( "if the car went 100 km/h ( rate )
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\n" ); document.write( "if the car took \"+5+-+x+\" hours ( time ), ( doesn't matter which time we could use \"x\" if we wanted, but we will use this one )
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\n" ); document.write( "These two multiplied together will equal a distance \"+470+-+y+\" , ( once again it doen't matter which distance, we could use \"y\" if we wanted )
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\n" ); document.write( "Now we would put the words into a formula,
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\n" ); document.write( "\"+rate%28time%29=+distance+\" = \"+100%285+-+x%29+=+470+-+y+\", this is the first equation
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\n" ); document.write( "Now we will use the other distance, time, and rate, to find the second equation
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\n" ); document.write( "If the car went 90 km/h ( rate )
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\n" ); document.write( "If the car took \"+x+\" hours ( time )
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\n" ); document.write( "If the car drove \"+y+\" km ( distance )
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\n" ); document.write( "Now replace \"r\", \"t\" and \"d\" with the other veriables
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\n" ); document.write( "\"+r%28t%29+=+d+\" = \"+90%28x%29+=+y+\", this is the second equation
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\n" ); document.write( "Now we can put these two equations side by side
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\n" ); document.write( "\"+system+%28+100%285+-+x%29+=+470+-+y%2C+90%28x%29+=+y%29+\"
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\n" ); document.write( "To make it easier, we will simplify the two equations
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\n" ); document.write( "Equation 1, \"+100%285+-+x%29+=+470+-+y+\", we can use the distribution to simplify this equation
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\n" ); document.write( "\"+100%285+-+x%29+=+470+-+y+\" = \"+highlight%28100%29%28highlight%285%29+-+x%29+=+470+-+y+\" = \"+highlight%28100%29%285+-+highlight%28x%29%29+=+470+-+y+\"
\n" ); document.write( "(remember the signs
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\n" ); document.write( "\"+100%285%29+-+100%28x%29+=+470+-+y+\" = \"+500+-+100x+=+470+-+y+\", we don't have to move anything right now, so this is the simplified form
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\n" ); document.write( "Equation 2, we will just multiply the \"90\" and \"x\"
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\n" ); document.write( "\"+90%28x%29+=+y+\" = \"+90x+=+y+\", this is simplified
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\n" ); document.write( "Now we can start solving for the two unknowns
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\n" ); document.write( "\"+system+%28+500+-+100x+=+470+-+y%2C+90x+=+y%29+\"
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\n" ); document.write( "This is a system of equations, the easiest way to solve this system is by substitution
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\n" ); document.write( "Since \"+y+=+90x+\", we can just simply replace \"y\" in the first equation with \"90x\"
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\n" ); document.write( "\"+500+-+100x+=+470+-+y+\" = \"+500+-+100x+=+470+-+%2890x%29+\"
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\n" ); document.write( "\"+500+-+100x+=+470+-+%2890x%29+\" = \"+500+-+100x+=+470+-+90x+\", now we can just solve for \"x\", we will move (-100x) to the right side
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\n" ); document.write( "\"+500+-+100x+=+470+-+90x+\" = \"+500+-+100x+%2B+100x+=+470+-+90x+%2B+100x+\" = \"+500+=+470+%2B+10x+\", now we will move \"470\" to the left side
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\n" ); document.write( "\"+500+=+470+%2B+10x+\" = \"+500+-+470+=+470+-+470+%2B+10x+\" = \"+30+=+10x+\", to find \"x\" we will divide each side by \"10\"
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\n" ); document.write( "\"+30+=+10x+\" = \"+30%2F10+=+10x%2F10+\" = \"+3+=+highlight%2810%29x%2Fhighlight%2810%29+\" = \"+3+=+cross%2810%29x%2Fcross%2810%29+\" = \"+3+=+x+\", \"+x+=+3+\"
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\n" ); document.write( "(remember \"x\" is the time in hours), we can replace \"x\" with \"3\" in the second equation, to find \"y\"
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\n" ); document.write( "\"+90x+=+y+\" = \"+90%283%29+=+y+\" = \"+270+=+y+\", \"+y+=+270+\", we can check our two answers by replacing \"x\" and \"y\" in the first equation
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\n" ); document.write( "x = 3
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\n" ); document.write( "y = 270
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\n" ); document.write( "\"+500+-+100x+=+470+-+y+\" = \"+500+-+100%283%29+=+470+-+%28270%29+\" = \"+500+-+300+=+470+-+270+\" = \"+200+=+200+\" (True)
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\n" ); document.write( "Here are the simplified equations with the numbers
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\n" ); document.write( "\"+system+%28+100%285+-+3%29+=+470+-+270%2C+90%283%29+=+270%29+\"
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\n" ); document.write( "\"+system+%28+100%282%29+=+200%2C+90%283%29+=+270%29+\"
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\n" ); document.write( "If we look at the formula, \"+rate%28time%29+=+distance+\"
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\n" ); document.write( "\"+system+%28+100%282%29+=+200%2C+90%283%29+=+270%29+\"
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\n" ); document.write( "This means that the car went 200 km at 100 km/h, and it went 100 km/h for 2 hours
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\n" ); document.write( "The car went 270 km at 90 km/h, and it went 90 km/h for 3 hours
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\n" ); document.write( "The distances add up to the total distance, as well as the time with the total time
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\n" ); document.write( "The car went 200 km at 100 km/h
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\n" ); document.write( "The car went 270 km at 90 km/h
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\n" ); document.write( "Hope I helped, Levi
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