# Preknowledge

 List here

Just like addition and subtraction, multiplication ($x$, $.$) and division (÷, $/$) are opposites of each other. Multiplying by a number and then dividing by the same number gets us back to the start again:

• $a$ × $b / b = a$
• $5$ x $4 / 4 = 5$

Sometimes you will see a multiplication of letters as a dot or without any symbol. Don’t worry, its exactly the same thing. Mathematicians are efficient and like to write things in the shortest, neatest way possible.

• $abc = a$×$b$×$c$
• $a$·$b$·$c = a$×$b$×$c$

It is usually neater to write known numbers to the left, and letters to the right. So although 4$x$ and $x$4 are the same thing, it looks better to write 4$x$. In this case, the “4” is a constant that is referred to as the coefficient of x.

# Extension exercise

 Commutativity for Multiplication

The fact that $ab = ba$ is known as the commutative property of multiplication. Therefore, both addition and multiplication are described as commutative operations.

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