How many gallons of gas would be used ?

Question

Justin drove 355 miles using 17 gallons of gas. At this rate how many gallons of gas would he need to drive 284 miles?

Answer 1

Christie--

 

I found the same answer as Barbara did in the previous solution.  However, I set up the problem slightly differently.  I tend to look at questions like these as conversion problems.  Here are the steps I followed:

 

1.  The first thing I would do is determine the ratio of miles traveled and gallons of gas consumed in the first sentence of the problem.  There are two ratios, identical in value:

          355 miles              or           17 gallons

           17 gallons                           355 miles

 

2. I will multiply one of these ratios by 284 miles to determine the number of gallons.  I will use whichever ratio (shown above) that allows me to cancel out the "miles" unit and end with a unit of gallons

          284 miles (17 gallons/355 miles).  

The miles will cancel out, and you are left with (284 x 17)/355 gallons.

This simplifies to 13.6 gallons.

 

I use this approach because working with the units helps guide me through the problem.  I always determine the ratios first.  Then I solve the problem by starting with the units I have (miles) and using the ratios or conversion factors one at a time until I end up with the units I want.

 

Sarah

Answer 2

This problem is a proportion.     355/284 = 17/G        cross multiply

 

355G = 284 x 17      355G = 4828       355G/355 = 4828/355      G = 13.6 gallons of gas.