Question

What is your average velocity if you drive a
distance of 306 km at a speed of 40 km/h, then
the same distance at a speed of 62 km/h?

Answer 1

What is your average velocity if you drive a distance of $306\,\mathrm{km}$ at a speed of 40 km/h, then the same distance at a speed of $62\,\mathrm{km/h}$?

$$v = \frac{S}{t}$$

where $v$ - an average speed, $S$ - a total distance, $t$ - a total time.

The total distance equals:

$$S = 306\,\mathrm{km} + 306\,\mathrm{km} = 612\,\mathrm{km}$$

The total time equals:

$$t = \frac{306\,\mathrm{km}}{40\,\frac{\mathrm{km}}{\mathrm{h}}} + \frac{306\,\mathrm{km}}{62\,\frac{\mathrm{km}}{\mathrm{h}}} = 12.59\,\mathrm{h}$$

Therefore:

$$v = \frac{612\,\mathrm{km}}{12.59\,\mathrm{h}} = 48.6\,\frac{\mathrm{km}}{\mathrm{h}} \cong 49\,\frac{\mathrm{km}}{\mathrm{h}}$$

Answer: $49\,\frac{\mathrm{km}}{\mathrm{h}}$