Average Rate calculations are common questions in National 5 exams. They seem to crop up in 3 forms: a table, a graph or a multiple choice question.
The example I work through in the video is from a table of values from an experiment. During a reaction, the volume of gas produced is measured at 30 second intervals and the results are displayed in the table provided.
The exam question asks you to calculate the average volume between 60 and 90 seconds (a 30 second time period). What you have to do is see how much gas is produced during this time period, and divide it by the time period (in seconds).
This will give you the rate, in cm3/s.