Question 1207775
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This is basically a "mixture" problem -- you are mixing miles driven at 40 mpg on the highway and miles driven at 25 mpg in the city.<br>
Here is a solution by a method that does not use algebra.  This method can be used to solve any 2-part mixture problem.<br>
All 900 gallons used on the highway at 40 mpg would make a distance of 36,000 miles; all 900 gallons in the city at 25 mpg would make a distance of 22,500 miles.<br>
Look at the three mileages 22,500, 30,000, and 36,000 (on a number line, if it helps) and observe/calculate that 30,000 is 7500/13500 = 5/9 of the distance from 22,500 to 36,000.<br>
That means 5/9 of the gallons were used at the higher rate.<br>
5/9 of 900 gallons is 500 gallons, so she used 500 gallons for her highway driving.<br>
500 gallons at 40 mpg is 20,000 miles.<br>
ANSWER: 20,000 miles<br>