A particular Chevy averages 20 miles per gallon in stop-and-go urban environments but averages about 28 miles per gallon on the interstate highways. On the way to Williamsburg, Virginia, the car traveled 784 miles and used 30 gallons of petrol. How many gallons were used driving on the interstate highways?

Question

Mathematics

Ibarra

18 August, 05:31

A particular Chevy averages 20 miles per gallon in stop-and-go urban environments but averages about 28 miles per gallon on the interstate highways. On the way to Williamsburg, Virginia, the car traveled 784 miles and used 30 gallons of petrol. How many gallons were used driving on the interstate highways?

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Answers (1)

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Anton · Answer 1

784=20x+28y

30 = x + y

x=urban

y=highways

so isolate a variable then substitute

30 - x = y

substitute:

784 = 20x + 28 (30-x)

784 = 20x + 840 - 28x

784-840 = 20x - 28x + 840 - 840

-56/8 = - 8x/8

7 = x

substitute back in

30 = x + y

30 = 7 + y

30-7 = 7 - 7 + y

y = 23