Melissa drove 250 miles using 9 gallons of gas. At this rate, how many gallons of gas would she need to drive 275 miles?

Question

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Answer 1

When you read a problem such as this, you should think about a proportion which says a is to b as c is to d.

 

This says two fractions are equal and we write it like this.

 

a/b = c/d

 

For this problem we have 250 miles with 9 gallons gas, and then 275 miles with an unknown number of gallons of gas.

 

So the proportion is 250 miles / 9 gallons = 275 miles / G gallons

 

And to solve the proportion, the first step is cross multiplication.

 

250G = 275(9)

 

G = 275(9)/250 = 9.9 gallons

 

The answer makes sense because for the additional 25 miles you would need a little more than 9 gallons of gas. If you got an answer that was less than 9 or a number like 2000, you would suspect that something was wrong with the answer.