‘Models’ introduces the concept and purposes of mathematical models. From working out the best trajectory for throwing a stone, rolling a pair of dice, and predicting population growth and the behaviour of gases, mathematical modelling can provide solutions to physical problems. Mathematicians apply scientific theories to an imaginary, simplified version of the problem where exact calculations are possible. Mathematical models can also be used to model how brains and computers work using a circuit model of computation. Finally it shows how mathematics is an abstract subject: it abstracts the important features from a problem and it deals with objects that are not concrete and tangible.