A car travels 20 miles in 12 hours. What is its average speed?

The average speed is 1.6666667 mph.

v = \frac{d}{t} = \frac{20}{12} = 1.6666667\ \text{mph}

How to work it out

1
Write down what you know: distance d = 20 miles, time t = 12 hours. You are asked for the speed v.
2
Use the formula speed = distance ÷ time:
$v = \frac{d}{t} = \frac{20}{12} = \frac{5}{3} = 1.6666667$
3
Answer with the unit: 1.6666667 mph.
4
The same formula rearranged: distance = speed × time (1.6666667 × 12 = 20 miles) and time = distance ÷ speed (20 ÷ 1.6666667 = 12 hours).

LaTeX source of the formulas on this page

\[ v = \frac{d}{t} = \frac{20}{12} = 1.6666667\ \text{mph} \]
\[ v = \frac{d}{t} = \frac{20}{12} = \frac{5}{3} = 1.6666667 \]

What is the speed if a car travels 20 miles in 12 hours?

The average speed is 1.6666667 mph.

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

5 miles.