document.write( "Question 161050: In a family there are 2 cars in a given week, the first car gets a average of 40 miles per gallon, and the second car gets 30 miles per gallon. the two cars combined drive a total of 1800 miles in that week, for a total gas consumption of 55 gallons. how many gallons were consumed by each of the two cars that week? \n" ); document.write( "
Algebra.Com's Answer #118661 by ptaylor(2198)\"\" \"About 
You can put this solution on YOUR website!
Let x=number of gallons consumed by the 40 mpg car
\n" ); document.write( "And let y=number of gallons consumed by the 30 mpg car
\n" ); document.write( "Now we are told that x+y=55---------------------------------eq1
\n" ); document.write( "Now we know that distance travelled by the 40 mpg car =40x
\n" ); document.write( "And the distance travelled by the 30 mpg car =30y
\n" ); document.write( "And we are also told that:
\n" ); document.write( "40x+30y=1800--------------------------------------------------eq2
\n" ); document.write( " divide each term of eq2 by 10 just to reduce the size of the numbers
\n" ); document.write( "4x+3y=180------------------------------------eq2
\n" ); document.write( " multiply eq1 by 4 (and we get4x+4y=220) and then subtract if from eq2:
\n" ); document.write( "-y=-40 divide each side by -1
\n" ); document.write( "y=40--------------number of gallons consumed by the 30 mpg car
\n" ); document.write( " substitute y=40 into eq1:
\n" ); document.write( "x+40=55 subtract 40 from each side
\n" ); document.write( "x=15 -------------------number of gallons consumed by the 40 mpg car\r
\n" ); document.write( "\n" ); document.write( "CK
\n" ); document.write( "30*40+40*15=1800
\n" ); document.write( "1200+600=1800
\n" ); document.write( "1800=1800\r
\n" ); document.write( "\n" ); document.write( "Hope this helps---ptaylor\r
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