Answer
The car will travel 324 miles on 12 gallons of gas.
Explanation
The car gets 27 miles per gallon of gas, that is, 1 gallon of gas gets the car 27 miles. In mathematical terms,
1 gallon of gas = 27 miles for the car
Let 12 gallons of gas get the car x miles.
1 gallon of gas = 27 miles for the car
12 gallons of gas = x miles for the car
Using simple mathematical relations, done by cross multiplying, we can obtain an expression that can be used to solve for x
1 × x = 27 × 12
x = 27 × 12 = 324 miles
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