How to calculate the average speed
Kapitoly: Average speed, Average car consumption
We calculate the average speed of, for example, a car by finding how many kilometres we travelled by car, how long it took us and dividing the two hdonots. For example, if we drove 200 kilometres and it took us 2 hours, we drove at an average speed of 100 kilometres per hour. So the basic formula is that the average speed PR is equal to
$$\Large PR=\frac{vzdálenost}{čas}$$
So
$$\Large\frac{200\ \mbox{km}}{2\ \mbox{h}}=100\ \mbox{km} / \mbox{h}$$
Other units
Another example: we drove 180 km and it took us 90 minutes. If we plug this into the formula, we calculate
$$\Large\frac{180\ \mbox{km}}{90\ \mbox{min}} = 2\ \mbox{km} / \mbox{min}$$
Notice that at this point we didn't get the speed in kilometers per hour, but in kilometers per minute! If we wanted to convert the speed into more common km/h, we have two options. The first is that instead of working with minutes in the formula, we convert them to hours. So 90 minutes is an hour and a half, so 90 min = 1.5 h. Now we can plug the values back into the formula:
$$\Large\frac{180\ \mbox{km}}{1{,}5\ \mbox{h}} = 120\ \mbox{km} / \mbox{h}$$
So we were driving at an average speed of 120 kilometres per hour. The second way is to say that if we drive an average of two kilometres per minute, we must drive sixty times as many kilometres in an hour that is 60 minutes. So we can multiply
$$\large 2\ \mbox{km} / \mbox{min} \cdot 60\ \mbox{h} = 120\ \mbox{km} / \mbox{h}$$