A car travels 390 km in 10 hours. What is its average speed?

The average speed is 39 km/h.

v = \frac{d}{t} = \frac{390}{10} = 39\ \text{km/h}

How to work it out

1
Write down what you know: distance d = 390 km, time t = 10 hours. You are asked for the speed v.
2
Use the formula speed = distance ÷ time:
$v = \frac{d}{t} = \frac{390}{10} = 39$
3
Answer with the unit: 39 km/h.
4
The same formula rearranged: distance = speed × time (39 × 10 = 390 km) and time = distance ÷ speed (390 ÷ 39 = 10 hours).

LaTeX source of the formulas on this page

\[ v = \frac{d}{t} = \frac{390}{10} = 39\ \text{km/h} \]
\[ v = \frac{d}{t} = \frac{390}{10} = 39 \]

What is the speed if a car travels 390 km in 10 hours?

The average speed is 39 km/h.

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

117 km.