We can calculate using unknown numbers by using letters in the place of the unknown numbers.

When we use letters instead of unknown numbers the answer will be an expression.

If we multiply n by 5 we get n × 5

We don't write a times sign in algebra, so we simplify n × 5 to 5n

(We write the number first to not mistake 5 × n for n^{5})

If we have 5 more than n we have n + 5

If we have 5 less than n we have n - 5

If we have n divided by 5 we have n ÷ 5 or

**Example 1: Apples cost 30p each. Write an algebraic expression for the cost of x apples.**

We need to multiply 30 by x.

30 × x = 30x

The total cost is 30x pence.

**Example 2: William has m marbles. Simon has 10 more marbles than William. Write an algebraic expression for the numbers of marbles Simon has. **

We need to add 10 onto m

The answer is m + 10

**Example 3: You buy 5 cups of tea for £pWrite an expression for the price of one cup of tea. **

We need divide p by 5

The answer is

£

**Try these:**