A car travels 310 miles in 4 hours. What is its average speed?

The average speed is 77.5 mph.

v = \frac{d}{t} = \frac{310}{4} = 77.5\ \text{mph}

How to work it out

1
Write down what you know: distance d = 310 miles, time t = 4 hours. You are asked for the speed v.
2
Use the formula speed = distance ÷ time:
$v = \frac{d}{t} = \frac{310}{4} = \frac{155}{2} = 77.5$
3
Answer with the unit: 77.5 mph.
4
The same formula rearranged: distance = speed × time (77.5 × 4 = 310 miles) and time = distance ÷ speed (310 ÷ 77.5 = 4 hours).

LaTeX source of the formulas on this page

\[ v = \frac{d}{t} = \frac{310}{4} = 77.5\ \text{mph} \]
\[ v = \frac{d}{t} = \frac{310}{4} = \frac{155}{2} = 77.5 \]

What is the speed if a car travels 310 miles in 4 hours?

The average speed is 77.5 mph.

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

232.5 miles.