Rate is the comparison of 2 quantities of different kind. If we buy chicken fillets, as an example, at a rate of R54/kg, it means that we have to pay R54 for 1 kg of chicken fillets. Now, if we want to buy 2,5 kg of chicken fillets, the price will be 2,5 times R54.
When you have to compare different types of rates, you need to re-write them in the same way. For example, if one car has a fuel consumption of 9 litres per 100 km and another car has a fuel consumption of 12 km per liter, you need to write them the same way. You can do that by writing the number of kilometres that each car can travel using 1 litre of fuel. Watch the video to see the explanation.
