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To answer what is rate, you can compare (a) to (c) with (d), which is actually a ratio. You will find that the rates are comparing 2 different quantities of different units. Thus,

Rate is the comparison of 2 different quantities of different units.

A car can travel 640 km with 8 litres of petrol. How much petrol does  the car needs so that it can travel 720 km? (Assume that the car's petrol assumption rate is always the same.)

Distance Travelled with 1 litre of petrol = 640 km/8 litres                                                               = 80 km/litres

Petrol needed to travel 720 km = 720/80                                                  = 9 litres

Read the questions below and try them out!

*1. Chef Wong uses 15 litres of oil per week in the restaurant. He always buys 3 5-litres bottles of oil which cost $9.50 each. How much will he save in a month if he decides to buy only 10-litres bottles of oil that will cost $15 each? (Assume that his oil usage is fixed and the remaining oil are always brought to next week.)

2. If a newspaper printing machine can print 50 000 newspapers in 2 minutes, how many machines of the same kind do you need to print 3 000 000 copies of newspapers in a minute?

* Not very much to do with rate. Think!