A car travels 420 km in 4 hours. What is its average speed?

The average speed is 105 km/h.

v = \frac{d}{t} = \frac{420}{4} = 105\ \text{km/h}

How to work it out

1
Write down what you know: distance d = 420 km, time t = 4 hours. You are asked for the speed v.
2
Use the formula speed = distance ÷ time:
$v = \frac{d}{t} = \frac{420}{4} = 105$
3
Answer with the unit: 105 km/h.
4
The same formula rearranged: distance = speed × time (105 × 4 = 420 km) and time = distance ÷ speed (420 ÷ 105 = 4 hours).

LaTeX source of the formulas on this page

\[ v = \frac{d}{t} = \frac{420}{4} = 105\ \text{km/h} \]
\[ v = \frac{d}{t} = \frac{420}{4} = 105 \]

What is the speed if a car travels 420 km in 4 hours?

The average speed is 105 km/h.

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

315 km.