1) 19s40centièmes = 0h0mn19s40centièmes => 19/60/60 = 0.00527777...77h et
40/60/60/60 = 0.000185185...185h donc 19s40centièmes = 0.0054629629...629h
200m = 0.2km
On fait le produit en croix
0.2 km => 0.0054629629...629h
x km => 1h
0.2 = 0.0054629629...629 x
x = 0.2/0.0054629629...629
x = 36.61 km/h
2) 1mn55s87centième = 60s + 55s + 0.0145s = 115.0145s
800 m => 115.0145
x m => 1s
Produit en croix = 800 = 115.0145x => x = 6.956 m/s soit 6.9 m/s
3) 2h7mn38s = 2.12722222...222h
distance = 2.12722222...222 x 19.836 = 42.19558 km soit 42.195 km