A car travels 30 km in 7 hours. What is its average speed?

The average speed is 4.2857143 km/h.

v = \frac{d}{t} = \frac{30}{7} = 4.2857143\ \text{km/h}

How to work it out

1
Write down what you know: distance d = 30 km, time t = 7 hours. You are asked for the speed v.
2
Use the formula speed = distance ÷ time:
$v = \frac{d}{t} = \frac{30}{7} = \frac{30}{7} = 4.2857143$
3
Answer with the unit: 4.2857143 km/h.
4
The same formula rearranged: distance = speed × time (4.2857143 × 7 = 30 km) and time = distance ÷ speed (30 ÷ 4.2857143 = 7 hours).

LaTeX source of the formulas on this page

\[ v = \frac{d}{t} = \frac{30}{7} = 4.2857143\ \text{km/h} \]
\[ v = \frac{d}{t} = \frac{30}{7} = \frac{30}{7} = 4.2857143 \]

What is the speed if a car travels 30 km in 7 hours?

The average speed is 4.2857143 km/h.

How far does it go in 3 hours at that speed?

12.857143 km.