Fuel efficiency in europe is commonly defined as fuel consumption per 100 [km]. an american car has a fuel efficiency of 32 [mi/gal) and a european car has a fuel efficiency of 5.2 [l/100 km). which car is more efficient?

The European car is more efficient (5.2 vs 7.35 L/100km)

Explanation:

To compare the two efficiencies we have to have them in the same units.

We have that 1 mi. is equal to 1.61 km and 1 gal is 3.785 litres.

The american car efficiency can be expressed as:

We calculate the amount of kilometers the car can make with one litre of fuel. To know the efficiency in L/(100 km) we have to rearrange the expression:

We know now that the american car consumes 7.35 L per 100 km, which is higher than the european car.

So, the European car is more efficient (5.2 vs 7.35 L/100km)