A rate is a ratio of two quantities with different units, like 40 meters in 8 seconds. A unit rate tells the amount for exactly 1 of the second unit: 40 ÷ 8 = 5 meters per second, which is a speed. Double number lines and ratio tables show a rate at many sizes, unit rates let us compare runners fairly, and ratio reasoning converts units, like minutes to seconds and meters to centimeters.