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# 2.8 Negative numbers and the use of brackets

Numbers smaller than zero (shown to the left of zero on the number line below in Figure 2) are called negative numbers. We indicate they are negative by enclosing them in brackets as shown in Figure 2. Figure 2 The number line

You may be used to seeing negative numbers indicated by the use of a minus sign ‘–’. However, because accountants conventionally use brackets so as to make it more obvious that a value is negative; this is the convention we adopt in this OpenLearn course. Negative numbers can be manipulated just like positive numbers and the calculator can deal with them with no difficulty as long as they are entered with a ‘–’sign in front of them.

## Box 3 Rules of negative numbers

The rules for using negative numbers can be summarised as follows:

Adding a negative number is the same as subtracting a positive

50 + (-30) = 50 – 30 = 20

Subtracting a negative number is the same as adding a positive

50 – (-30) = 50 + 30 = 80

Multiplication and division

A positive number multiplied by a negative gives a negative

20 x -4 = -80

A positive number divided by a negative gives a negative

20 / -4 = -5

A negative number multiplied by a negative gives a positive

-20 x -4 = 80

A negative number divided by a negative gives a positive

-20 / -4 = 5

Try to confirm the above rules for yourself by carrying out the following activity either manually or by means of a calculator.

## Activity 7 Use of negative numbers in maths operations

Calculate each of the following. (In this activity we will assume the convention that if a number is in brackets it means it is negative.)

1. (2) x (3)
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6

1. 6 – (8)
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14

1. 6 + (8)
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(2)

1. 2 x (3)
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(6)

1. (8) / 4
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(2)

1. (8) / (4)
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