Bonjour,
1) 30 m => 15 s
x m = 1 s ?
x = 1 × 30/15 = 2 m/s => réponse b
2) 100km => 2h
x km = 1h ?
x = 1 × 100/2 = 50km/h => réponse b
(50 km/h = 50/3,6 = 13 m/s)
3) 4000m => 2h
4000m = 4km
Donc : 4km => 2h
x km => 1 h ?
x = 1 × 4/2 = 2 km/h => réponse c