Question 1202518
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the distance a car travels varies directly with the amount of gasoline it uses. 
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The language clearly becomes, with these assigned variables,
k, variation constant
d, distance travel
x, amount of fuel used
;
the equation {{{d=kx}}}.


The part which follows in the description is that x=9 corresponds to d=207; so you can find the value for k.



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Notice the units for each number involved in the question.
13 gallons of gasoline;
9 gallons gasoline for 207 miles;
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Question is "how many miles travel if 13 gallons...?"
Begin with the 13 gallons:


{{{13*gallons*(207/9)(miles/gallons)}}}


{{{((13*207)/9)*((cross(gallons)*miles)/cross(gallons))}}}


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