A car travels 100 miles in 8 hours. What is its average speed?

The average speed is 12.5 mph.

v = \frac{d}{t} = \frac{100}{8} = 12.5\ \text{mph}

How to work it out

1
Write down what you know: distance d = 100 miles, time t = 8 hours. You are asked for the speed v.
2
Use the formula speed = distance ÷ time:
$v = \frac{d}{t} = \frac{100}{8} = \frac{25}{2} = 12.5$
3
Answer with the unit: 12.5 mph.
4
The same formula rearranged: distance = speed × time (12.5 × 8 = 100 miles) and time = distance ÷ speed (100 ÷ 12.5 = 8 hours).

LaTeX source of the formulas on this page

\[ v = \frac{d}{t} = \frac{100}{8} = 12.5\ \text{mph} \]
\[ v = \frac{d}{t} = \frac{100}{8} = \frac{25}{2} = 12.5 \]

What is the speed if a car travels 100 miles in 8 hours?

The average speed is 12.5 mph.

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

37.5 miles.