# Math Expressions. How to write simple mathematical expressions.

When writing down expressions in algebra you need to write them down in a specific way. In algebra a letter can be used to stand for an unknown quantity.  Adding and taking away are straightforward:

x -7 means x take away 7

but times and divide can be harder to do:

7x mean 7 times x

x/7 means x ÷ 7

Let’s have a look at a real life example.

Example 1

A fish pod contains a large amount of fish. Write down an expression if:

a)      1 more fish is added to the pond

b)      2 fish are taken out of the pond

c)       3 times the original amount of fish are added to the pond

d)      the amount of fish in the pond is divided by 4

First of all use the letter f to stand for the amount of fish originally in the pond.

a)      f + 1 since there are no special rules for adding.

b)      f – 2 since there are no special rules for taking away.

c)       3f since if you are multiplying the number comes first and the letter comes second.

d)      f/4 since you always write a division as a fraction (with a line).

Example 2

A line has a length of y cm. Write down an expression if the length of the line is trebled.

Here we are multiplying the length of the line by 3.

So y×3 times by 3 can be written as 3y.

Example 3

Another line has a length of z cm. Write down an expression if the length of the line is halved.

Halving is the same as dividing by 2.

so Z ÷divided by 2 can be written as z/2.

Top Tips:

Just remember when you are multiplying put the number first followed by the letter, and leave out the multiply sign.

Use a line for dividing.

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