Jack travelled 2/3 of a journey at speed of 60 km/h for 4 hours. What average speed must he travel at for the rest of the journey in order to complete the whole journey in 5 hours?

km/h

2/3 of the journey: 60 × 4 = 240 km

Then, the total distance of the whole journey: 240 ÷ 2/3 = 240 × 3/2 = 360 km

Distance for the rest of the journey: 360 - 240 = 120 km

Time for rest of the journey: 5 - 4 = 1 h

Recall the formula: Average Speed = Total Distance ÷ Total Time

Thus, average speed for the rest of the journey: 120 ÷ 1 = 120 km/h