A car travels 100 miles in 12 hours. What is its average speed?

The average speed is 8.3333333 mph.

v = \frac{d}{t} = \frac{100}{12} = 8.3333333\ \text{mph}

How to work it out

1
Write down what you know: distance d = 100 miles, time t = 12 hours. You are asked for the speed v.
2
Use the formula speed = distance ÷ time:
$v = \frac{d}{t} = \frac{100}{12} = \frac{25}{3} = 8.3333333$
3
Answer with the unit: 8.3333333 mph.
4
The same formula rearranged: distance = speed × time (8.3333333 × 12 = 100 miles) and time = distance ÷ speed (100 ÷ 8.3333333 = 12 hours).

LaTeX source of the formulas on this page

\[ v = \frac{d}{t} = \frac{100}{12} = 8.3333333\ \text{mph} \]
\[ v = \frac{d}{t} = \frac{100}{12} = \frac{25}{3} = 8.3333333 \]

What is the speed if a car travels 100 miles in 12 hours?

The average speed is 8.3333333 mph.

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

25 miles.