Derek starts by explaining how Section C concerns the number system and how addition, subtraction, multiplication and division works with whole numbers. He draws attention to how these ideas can be explained by making connections between with the operations by using language (formal/ informal), various pictures like the Number Line method and concrete objects including Base Ten Blocks. For each of the operations there are three chapters which Haylock outlines: the first considers all the where the operation might apply, the second looks at the mental and informal methods which children might use to make calculations and the third in the sequence looks at more formal written methods.

The next stage of the video shows Derek giving an example of subtraction to explain how mathematic symbols can be connected, looking at different variations of the calculation dependent on situation. He explores use of the Number Line to show the potential of informal methods with teaching children. He then explains Chapter 9 of the book is about the formal methods of the vertical layout that you would use to complete subtractions using methods such as subtraction by decomposition. Derek reinforces that connections with number plots and other methods should be used in conjunction with formal methods like this. The video ends with Derek stating that children should be learning mathematics by making connections.