Why do I need unit conversion to plan a road trip?

Stretch the trip, change the car's mpg, and watch the fuel and cost update.

Challenge: Plan a trip of at least 300 miles that costs $50 or less in fuel. The box under the picture turns green when you get it.

Stuck? Pick one of the examples from the “Try an example” menu, or press “New example.”

Unit conversion is multiplying by fractions that equal 1. Since $1\ \text{mi} = 1.609\ \text{km}$, the fraction $\frac{1\ \text{mi}}{1.609\ \text{km}}$ is exactly 1, and multiplying by it changes the units without changing the distance.

After that, the trip is two steps of arithmetic:

$$\text{gallons} = \frac{\text{miles}}{\text{mpg}}, \qquad \text{cost} = \text{gallons} \times \text{price}$$

Enter the distance in km or miles, your car's mpg, and the local price per gallon. The fuel bar shows how much of a typical 16-gallon tank the trip uses.

• Real-world fuel economy is often 10–15% worse than the sticker at highway speeds.
• Link the fuel cost into the sale-price exhibit to add tax.