Question 1168128
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A family has two cars. The first car has a fuel efficiency of 40 miles per gallon of gas 
and the second has a fuel efficiency of 25 miles per gallon of gas. 
During one particular week, the two cars went a combined total of 1575 miles, for a total gas consumption of 45 gallons. 
How many gallons were consumed by each of the two cars that week?
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Let x be the number of gallons were consumed by the first car.

Then the number of gallons consumed by the second car is  (45-x).


The distance traveled by the first car is 40x miles.

The distance traveled by the second car is 25*(45-x) miles.


The total distance equation is

    40x + 25*(45-x) = 1575  miles.


From this equation, express x and calculate

    x = {{{(1575 - 25*45)/(40-25)}}} = 30.


<U>ANSWER</U>.  The first car consumed 30 gallons of fuel.  The second car consumed the rest (45-30) = 15 gallons.
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Solved.