A car uses 4 litres of petrol for 60 km. Its mileage in km per litre is:

1. Mileage is distance divided by fuel used. 2. Here that is 60 km for 4 litres. 3. So the mileage is 60 / 4. 4. That is 15 km per litre. 5. This constant ratio is what makes distance and petrol directly proportional: 12 litres would carry the car 180 km. _Source: syllabus Maths, Ch 11 'Direct and Inverse Proportions', S11.2 Direct Proportion_