A car starts a 360 km journey with a full tank. For the first 150 km, it travels at 60 km/h. Due to fuel reduction, the speed drops by 10 km/h for the next 120 km. For the remaining journey, it further slows by 10 km/h. Estimate the average speed for the whole journey.
Show answer & explanation
Correct answer: C
Explanation
Speed for the first 150 km = 60 km/h
Time = 150 / 60 = 2.5 hours
Speed for the next 120 km = 50 km/h
Time = 120 / 50 = 2.4 hours
Remaining distance = 360 − 150 − 120 = 90 km
Speed = 40 km/h
Time = 90 / 40 = 2.25 hours
Total distance = 360 km
Total time = 2.5 + 2.4 + 2.25 = 7.15 hours
Average speed = 360 / 7.15 = 7200 / 143 ≈ 50 km/h