A car travels 420 miles in 10 hours. What is its average speed?

The average speed is 42 mph.

v = \frac{d}{t} = \frac{420}{10} = 42\ \text{mph}

How to work it out

1
Write down what you know: distance d = 420 miles, time t = 10 hours. You are asked for the speed v.
2
Use the formula speed = distance ÷ time:
$v = \frac{d}{t} = \frac{420}{10} = 42$
3
Answer with the unit: 42 mph.
4
The same formula rearranged: distance = speed × time (42 × 10 = 420 miles) and time = distance ÷ speed (420 ÷ 42 = 10 hours).

LaTeX source of the formulas on this page

\[ v = \frac{d}{t} = \frac{420}{10} = 42\ \text{mph} \]
\[ v = \frac{d}{t} = \frac{420}{10} = 42 \]

What is the speed if a car travels 420 miles in 10 hours?

The average speed is 42 mph.

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

126 miles.