To determine which car has the greatest efficiency, we need to consider the fuel efficiency in terms of distance traveled per unit of fuel consumed, as well as the weight of the car.
Here are the cars you mentioned with their respective efficiencies:
- 1,200 kg car that travels 15 km per liter: Efficiency = 15 km/l
- 900 kg car that travels 20 km per liter: Efficiency = 20 km/l
- 900 kg car that travels 15 km per liter: Efficiency = 15 km/l
- 1,200 kg car that travels 20 km per liter: Efficiency = 20 km/l
From this data, we can see that the two cars with the highest fuel efficiency are the 900 kg car that travels 20 km per liter and the 1,200 kg car that travels 20 km per liter.
However, if we're looking purely at efficiency in terms of distance per fuel consumption, the 900 kg car that travels 20 km per liter is the most efficient overall because it has the highest distance per liter of fuel consumed and is also lighter than the alternative 1,200 kg option achieving the same efficiency.
So, the answer is: The 900 kg car that travels 20 km per liter has the greatest efficiency.