Bonjour,
1) vitesse = distance ÷ temps
donc temps = distance ÷ vitesse
= 60 km ÷ 140 km/h
= 3/7 h
2) temps = 60 km ÷ 100 km/h = 0,6 h = 3/5 h
3/7 + 3/5 = 15/35 + 21/35 = 36/35 h
3) vitesse = distance ÷ temps
= 2 × 60 km ÷ 36/35 h
= 116,6666..... km/h
