Demi traveled 480 miles in 6 hours. What was her average speed in miles per hour?

The classic formula relating rate (also called “average speed”), time and distance is:

r x t = d

That is, rate x time equals distance. The problem statement asks us for the rate and gives us the time (6 hours) and distance (480 miles). We can substitute those values into the classic formula:

r x 6 hours = 480 miles

To solve for r, we divide the terms on both sides of the equal sign by 6 hours. This works because the two sides are equal and we treat them equally by dividing the two sides by the same amount, so the results should be equal. Thus we get:

r = 480 miles/6 hours

Simplifying, we get:

r = 80 miles/hour

To CHECK, let’s plug back into the original equation:

r x t = d

80 miles/ hour x 6 hours = 480 miles

480 miles = 480 miles which is true. Yippee.