When writing down expressions in algebra you need to writethem down in a specific way. In algebra a letter can be used to stand for anunknown quantity.  Adding and taking awayare 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 anexpression 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 tothe 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 offish originally in the pond.

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

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

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

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

Example 2

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