Sometimes in Maths numbers can be replaced by letters but do not be put off by letters!

Letters are used for a special type of Maths, called **algebra. **

When we use algebra, we use **'formula'**.

Formula is a concise, simple way of showing information with symbols.

There are lots of formulas in Maths to find.

For example: area, perimeter and circumference.

**Example 1:**

If a = 6, b = 3 and c = 7, calculate the value of:

1. a + b = 2. a - b = 3. c + b - a =

**Solution:**

1. a + b

= 6 + 3 = 9

2. a - b

= 6 - 3 = 3

3. c + b - a

= 7 + 3 - 6 = 4

**Reminders:**

There are some rules to remember when using formula:

**We write:**

2 x a as 2a

a x b = ab

a ÷ b as a/b

**Example 2:**

If p = 6, q = 12, r = 4 and s = 3 calculate the value of:

1. rs 2. 2r + 3s 3. s/3

**Solution:**

1. rs = r x s

= 4 x 3 = 12

2. 2r + 3s = 2 x r + 3 x s

= 2 x 4 + 3 x 3

=8 + 9 = 17

3. s/3 = 3 / 3

= 1