C to F: double it, add 20. (Not exact, but easy to do and remember)
Distances: Think track and field, which has converted in the US. A 5k run is 3.1 miles. A 10k run is 6.2 miles.
Car indicates 50 k/h, you're going 31 m/h.
Car indicates 100 k/h, you're going 62 m/h.
But, who really cares, if...