Here's a diagram. Now suppose I want to find the ... This is not the correct way to solve this problem — I actually remember making this exact mistake when I was an undergraduate student.

Bar modelling is not a method of calculation. It provides a diagram to help understand what working out should be done to solve a problem. Bar modelling is used to help understand how to solve ...

You may be asked to solve problems using Venn diagrams in your exam. It is really important you draw the Venn diagram and add information as you go along. This will help you keep an overview of ...