Final answer:
Sam's car gets 21 miles per gallon. By cross-multiplying the given ratio of 7 miles per 1/3 gallon to find the mileage for one full gallon, we determine the car's gas mileage to be 21 miles per gallon.
Step-by-step explanation:
To calculate the gas mileage per gallon for Sam's car, we use the proportion that Sam's car gets 7 miles for every 1/3 gallon of gas. We want to find out how many miles the car can go on one gallon (1/1 gallon). To solve this, we can set up a ratio:
7 miles / (1/3 gallon) = x miles / (1 gallon)
By cross-multiplying, we have:
7 miles × 1 gallon = x miles × (1/3 gallon)
Now, we solve for x:
7 miles/gallon = 3 × 7 miles/gallon
7 miles/gallon × 3 = 21 miles/gallon
Therefore, Sam's car gets 21 miles per gallon.