Welcome to this deck on substitution. Substitution in algebra is like having a substitute teacher. The usual teacher, represented by a letter, is away, and a number comes in to take their place. We're going to learn how to replace these letters with numbers to find the value of expressions and formulae.

Let's start with a simple example. Imagine you have the expression 'a plus 5'. If we are told that 'a' has a value of 3, we just replace the letter 'a' with the number 3. The expression becomes 3 plus 5, which equals 8.

Remember that in algebra, when a number is right next to a letter, it means you multiply them. For example, the term '4p' means 4 times p. So if p was 2, 4p would be 4 times 2, which is 8.