How to define indirect variation.
How to define direct variation.
Understanding the concept of genetic variation.
How to define joint and combined variation.
How to use similar triangles to measure the height of objects.
How to tell if two variables vary inversely.
How to tell if two variables vary directly.
The fast evolution of species with a common ancestor.
Understanding the variations in the structure and composition of individual molecules with the same chemical formula.
How to graphically depict the variation in the energy of substances involved in reactions as they progress from reactants to products.